EVEN IN THE AGE OF VIAGRA, WHEN BLUE JOKES ABOUT THE LITTLE BLUE PILL can be heard at every turn, impotence is rarely a topic among men. It is not for lack of interest or experience. Most of us have known our sexual machinery fails to operate -and some of us have known it more then others.

A few years ago, it became all too evident that I was edging toward impotence. Erections had become less then rock hard and, even worse, less than dependable. The prospects were dire. Up to that point, like most men, I had avoided learning very much about how the penis works, what can go wrong, and what can be done about it. But now I had the best of reasons to find out. I made an appointment with E. Douglas Whitehead, M.D., an associate clinical professor of urology at the Albert Einstein College of Medicine in New York City, whose specialty is impotence. It was the start of an adventure by turns painful, embarrassing, and enlightening.

On my first visit, I found myself in a waiting room filled with men whose noses were buried in magazines - no exchanging of symptoms in this office. At age 67, I was in the majority, though several patients were in their early 50s and a few much younger than that.

We were the exceptions: Less than 10 percent of the estimated 30 million men in the U.S. with some form of erectile dysfunction, or E.D., as it's known in medical circles, ever seek medical help. The rest view impotence as inevitable, assume that nothing can be done, or are too embarrassed to talk about it, even with a physician. In our culture, sex is for the young; it is perceived as unseemly, even unnatural, in the old. We're supposed to be sexual, and those who refuse to be so are branded dirty old men or shameless hussies and made the butt of jokes. No wonder so many men keep it to themselves.

Given these feelings of shame and despair and society's disapproval, many impotent men and their partners forswear sex altogether. They have no appetite for the extensive menu of pleasurable alternatives to intercourse. My wife and I were under no such constraints, but I was still committed to the main course.

When I was finally ushered into Dr. Whitehead's office, I told him that I wanted to cut right to the chase and talk about all the treatment options that were available to me. "Not so fast," he replied firmly. "Diagnosis before treatment. Impotence can be an indication that something else is wrong."

Age per se is never the villain - some men in their 80s can still achieve erection - but as we get older, we are more likely to encounter physical illnesses or undergo medical treatments that cause E.D., including vascular disease, diabetes, hypertension, and prostate cancer surgery. Among men with E.D. in their 30s, 40s, and early 50s, psychological factors - depression, stress, and performance anxiety - play a larger role. Brought up to equate sexual achievement with our manhood; we react to the first sign of trouble with dread. For some, the failure becomes a self-fulfilling prophecy. [For more information on psychologically based impotence, see "When It's All in Your Head" on the AARP Modern Maturity website.]

In my case, I was pinning my hopes on a physical cause, a shortage of the male hormone testosterone, which is rare but might be easily repaired with a testosterone patch or injection. Whitehead tested my blood. No luck on the patch, he reported - my testosterone level was normal.

Now the fun began. I was introduced to the RigiScan system, a take-home exam that monitors rigidity and tumescence. Men normally experience multiple erections every night during the rapid-eye-movement stages of sleep. RigiScan measures how often these erections occur, how long they last, and how rigid they are. If I passed, it would mean that my impotence had a psychological rather than a physiological cause.

A reasonable man might have rooted for a normal result and a clean bill of health physically; I took the opposite tack. I felt that a psychological problem would represent a personal failure, something I wasn't man enough to control. I wanted a quick fix, not a season on a therapist's couch.

So for three nights I shared the bed with a machine and a somewhat bemused wife. I slept on my left side, with a heavy, battery-filled monitor strapped to the inside of my left thigh. My penis was encircled by two loops - one at the tip, one at the base - that were connected by wires to the monitor. Any penile action would be picked up by the loops and passed on to the monitor.

The result: My erections had been infrequent and poorly maintained. I inwardly cheered - I had escaped the couch. Now Whitehead had to determine the cause of the problem. He told me to undress. The first step, he said, would require a test of my erectile nerves. As I sat there exposed, a young female aide walked in and proceeded to touch various parts of my penis with a metal contraption. Each time she did, she inquired whether I was feeling any vibration. I told her I was definitely picking up her vibes.

As I was discovering, the erection process is complex. Within the penis are two side-by-side cylinders called the corpora cavernosa that are filled with spongy tissue and it expands. To prevent round-the- clock erections, which were not part of our design, smooth-muscle cells keep the arterial blood flow to a steady trickle and the tissue relatively empty.

When we're sexually stimulated, the brain sends the appropriate signal to the penile nerves, which release chemicals to relax the smooth muscles. That increases blood flow into the penis, creating an erection. Meanwhile, the veins that normally drain excess blood from the penis are squeezed shut by the expanding cylinders, so the blood stays put and the erection is maintained.

The vibration test ruled out nerve damage as a cause of my impotence. Whitehead's next step was to check blood flow to my penis, which required that I have an erection. He injected my penis with a syringe of alprostadil to relax the smooth muscles. He said it would hardly hurt. I didn't believe that for a second, and I was right. But the pain was bearable and short-lived. He said an erection would occur in minutes, and on his way out, he handed me an X-rated magazine in case I wanted to hurry things along, I did and it did.

Another aide (male, this time) entered the room with an ultrasound machine that measured the speed of blood flow and the width of the cavernosal arteries in my penis. The result: Mt flow was impaired, which is the most common cause of E.D. Finally, the villain had been identified and we could at last move on to treatment.

Concern about impotence is at least as old as the Bible, were Sarah wonders about her life with Abraham: "After I am waxed old, shall I have pleasure, my lord being old also?" Imaginative remedies have been around at lest as long, ranging from ground-up rhinoceros horn to snakeroot resin to Spanish fly, but urologists, including Whitehead, says they don't test out.

He proposed three other options that do work. One consists of an eight-inch plastic tube that you place over the penis. An attached pump sucks the air from the cylinder; this creates a vacuum that draws blood into the penis, producing an erection. An elastic band is placed at the base of the penis to hold the blood in. The device is safe (as long as you remove the band after 30 minutes) and the erection achieved is adequate. I took one look, however, and decided it was too cumbersome and not exactly conductive to romance.

The second option required surgery. Two cylinders comparable to the corpora cavernosa are planted in the penis and attached to a reservoir of liquid into the cylinders, producing an erection. Clearly this would be a court of last resort. I couldn't imagine setting up all that machinery in my innards.

The third option, which Whitehead recommended, was that I inject myself with alprostadil, the drug I had already sampled. The product, available as Caverject , comes with syringe, powder, liquid, and sterile swipe. Alprostadil worked fine, within limits. Erections arrived in short order and lasted about an hour, but I was never comfortable with the needle. It hurt. In any event, since my E.D. was limited, I used it only a few times a month and kept my eyes open for something better.

In January 1997, I thought I'd found it. A new treatment, Muse, delivered a pellet of alprostadil through an applicator that you inserted into the tip of the penis - definitely better than an injection. I gave Muse a try, but it didn't do the job.

Then, in April 1998, Viagra (Sildenafil) burst upon the scene. Urologists were inundated by new patients and by existing patients like me who wanted to switch. Finally, no needles, no pumps, no applicators, no mechanical parts. Contrary to popular opinion, Viagra doesn't cause an erection (it's still up to you and/or your mate to do that), it blocks the action of an enzyme that erodes erections, allowing improved blood flow to the penis.

But Viagra is not perfect: (1) it works for only 70 percent of patients; (2) it takes up to an hour for the body to absorb it; (3) you can't take it if you're on certain heart-disease medications; and (4) there are temporary side effects such as a flushed face, altered color perception, or a headache. Nevertheless, by early May, Viagra prescriptions were running 300,000 a week; by October they reached 4.5 million, breaking all records for new drug sales.

When I walked into Whitehead's office after trying it, he gave me the greeting that's become part of his office routine: "Ah, I see you're wearing your Viagra smile." The pill worked fine. I was pleased, my wife was pleased, Whitehead was pleased.

We were not alone, as I discovered during a visit with some members of an Impotence Anonymous chapter. (The organization has about 35 support groups around the country. Call 800-669-1603 for the one nearest you.) I asked if any of them had taken Viagra. They all had and they were all enthusiastic. Frank, 62, an engineer, had tried Caverject without success. David, 55, a psychologist who had lost a penile nerve to prostate surgery, found the injections effective but painful. Viagra worked for both. [Note: It has not been known to work for many men with true nerve damage. - Ed,] Now, when David's wife sees his face flushed, he said, "She knows the signs - it's a Viagra night!"

Since its introduction, Viagra has become a staple of the popular culture, celebrated in jokes and TV sitcoms, spreading the word that this embarrassing condition is widespread and treatable. And by enticing men to take that first step into a doctor's office, it has also saved lives. Routine tests have led to early to early diagnosis of diseases such as diabetes, heart disease, and prostate cancer. The birth-control pill performed a similar service for women, luring them to doctors' offices where in many cases Pap tests disclosed cervical cancer.

Now, more anti-impotence drugs are on the way, including pills, lozenges, even gels and sprays. [For a look at the new products, see "Beyond Viagra" at www.aarp.org/mmatury.] Indeed, my success with Viagra and the prospect of ever-better sex through chemistry in the years ahead have made me accepting of my E.D. lot. Well, almost.

After years of impotence, your husband has been rescued by Viagra or one of the other E.D. treatments. Is everybody happy? Not necessarily. Some female partners frown on Viagra because they don't want their children conceived with the help of a drug. Others never cared that much for intercourse or lost their enthusiasm over the years. Postmenopausal physical changes, including a thinning of the vagina's walls and a shortage of lubrication, can make intercourse painful.

Now their Viagra-empowered husbands are ready to turn back the clock, and some wives are balking. There are reports that a number of husbands have taken on mistresses or even sued for divorce. Long-abstinent couples may have to develop a new sexual equilibrium, says Marilyn K. Volker, E.D., a 53-year-old sexologist in Coral Gables, Florida, and that can take time. She urges them to establish a routine of close, intimate expressions of love before they try to resume intercourse. "I define the sexual experience as the genitals connected to the brain - with the heart in between," she says.

Volker's husband, David Yoblick, 58, has had erection problems since 1989, the result of diabetes and a heart condition. He uses Viagra now - and it has definitely empowered him. "It was awesome to regain the possibility for intercourse after nine years," she says. "We both cried."

Not that their sex life up to that point had been so bad. "Because of the erection problem, David actually became a better lover," she says. "When he takes Viagra, the sex is very much penis-focused. When he doesn't, he's more, well diffuse. I like that better."   - R.W.S.