Some call it that sex pill. Harold Dennis, 61, calls it something close to a miracle.

"I've been impotent since 1986. But last night, I felt good." he puts his arm around his wife, Juanita, and flashes a big grin.

"It was very satisfactory."

In the three weeks Viagra has been available, drugstores nationwide have filled an estimated 150,000 prescriptions. Across America, men have found satisfaction in a way they haven't for years and both men and women engaged in the eternal scrimmage of the sexes have found the playing field shifting once again.

There are other treatments for impotence. Vacuum pumps, inflatable implants and drugs that are injected into the penis or plunged down theurethra but their disadvantages are obvious.

Viagra is something new: The first pill that makes erections possible. Take the tablet. Wait a half hour. Add a little old-fashioned sexual stimulation. And things begin to happen, perhaps for the first time in a long while. No wonder doctors can't write prescriptions fast enough.

"It's the biggest thing since the Beatles,'' said Rafael Wurzel of New Britain General Hospital in the northeastern state of Connecticut. He has already made out more than 300 Viagra prescriptions.

"There are about 30 million guys out there" with "erectile dysfunction" as impotence is called now by most doctors and "hardly any will acknowledge the problem and get help," Wurzel said. "All of a sudden, I see this taboo totally debunked because of Viagra."

Overnight, patients he'd seen for years for kidney stones, prostate woes, bladder tumors, whatever, began calling him to talk about this other little matter they'd never gotten around to mentioning.

Typical of his patients isBernard, 58, a retired construction worker who, like many taking the pill, doesn't want to see his name in the newspaper. Cancer and emphysema, plus the side effects of his medicines, have made erections unpredictable for him the past four years, but he's still grinning about the first time he took Viagra. "I didn't say a word to my partner before," he said. "But afterward, she asked what got into me. This took me back 10 years. It's changed my life. It's given me more self-confidence. I feel good about who I am."

Doctors generally appear to be prescribing the drug for men like Bernard who have clear physical reasons for their impotence. Among the most common causes are diseases that damage the nerves or interfere with blood flow to the penis. These include high blood pressure, diabetes, clogged arteries, multiple sclerosis and reactions to medications.

Among those most interested in Viagra are men who have had their cancerous prostate glands removed. The operation often snips nerves essential forerections. Many of these men are still vigorous and healthy, and still interested in sex. But only about 25 per cent to 40 per cent are likely to be helped by Viagra.

While specialists are delighted to have something new to offer their patients and talk-show hosts are rushing to line up guests, some observers worry about Viagra's effects beyond the mechanics of erection.

What will it do to couples' relationships? What about the curious who want to see if it revs up normal sexual prowess? How much sex should an aging man expect, anyway? Who will pay for it?

The company which makes Viagra, stresses that it's not quite a sexual fountain of youth.

"Viagra restores. It doesn't create," said spokesman Andy McCormick. "A 55-year-old man taking viagra would report a return of desire consistent with a healthy 55-year-old man, not to the level of a 22-year-old."