WASHINGTON (AP) _ Impotence is neither inevitable nor untreatable and, with proper therapy, men can be sexually active for a lifetime, a National Institutes of Health panel of experts concluded Wednesday.

The 14-member committee, in a statement summarizing the recommended medical care for patients with impotence, said that age alone is not the cause of the male dysfunction and that the condition can be successfully treated by several different therapies.

''One of the myths is that the elderly become impotent because they are old. That is not true,'' said Dr. John C. Beck, a professor of geriatrics at the UCLA School of Medicine and a member of the panel.

Impotence is caused by physical or psychological conditions that can be treated successfully, the committee said, but it all depends upon a willingness of patients to accept frank, comprehensive discussion of their sexual history, to undergo thorough medical examinations and to seek out knowledgeable physicians.

What the committee did not find was the proven value of any of the traditional herbal or over-the-counter treatments for impotence. The panel said they had no scientific evidence that such things as rhinoceros horn or plant extracts can work as aphrodisiacs.

''For thousands of years there have been various things proposed as aphrodisiacs,'' said Dr. William J. Bremner, a professor of medicine at the University of Washington. ''Nothing that can be taken by mouth has ever been proven to be effective for impotence.''

Another committee member, Dr. Thomas J. Rohner Jr., a professor at the Pennsylvania State University College of Medicine, noted: ''There is no pill that you can take.''

Impotence, or erection dysfunction as the committee preferred to call it, affects 10 million to 20 million American men, with perhaps 10 million others having partial dysfunction, the panel said.

Though the problem for decades was accepted as the natural result of age and few men sought medical solutions, that perception is changing, said Dr. Michael Droller, chairman of the committee and chairman of the urology department at the Mount Sinai Medical Center in New York.

''Increasingly, more and more men are seeking treatments that will allow them to return to a satisfactory level and range of sexual activities,'' he said.

Treatment for impotence, the panel said, should start with a careful sexual and medical history and that psychological therapy, for both the patient and his principal partner, should be a part of the program.

Patients may have to seek out experts in the field, the panel said, because primary physicians often are untrained in impotence treatment.

''Erectile dysfunction is poorly understood by the general population and by most health-care professionals,'' the committee report said.

Chronic physical conditions, or drugs to treat these conditions, often are the cause of impotence, and the committee said physicians should ''inquire into the sexual functioning of their patients and be prepared to offer counsel.''

About 25 percent of all impotence, the committee said, is caused by drugs given to treat other conditions.

The problem can be in the mind, the report said.

''Psychological therapy alone is appropriate for patients in whom no organic cause of erectile dysfunction is detected,'' the study said. ''Working with the sexual partner is useful in improving the outcome of therapy.''

Medical therapy should start with the simplest procedure and more invasive treatments, such as surgery, should be used only when other techniques fail or appear inappropriate.

Among the approved therapies now available:

-Injection of drugs that cause vessels in the penis to dilate and become engorged with blood, a necessary event for erection. This is successful in 80 to 90 percent of cases, panel members said.

-Vacuum devices that force blood into the penis and cause it to become erect. This, also, has been shown to be highly effective.

-Constriction devices that pinch off return blood flow from the penis, causing blood to pool in the organ and force an erection.

-When impotence is caused by blood vessel flaws, surgery can sometimes correct the condition. But the panel said that such procedures are ''investigational'' and should be performed only by trained specialists.

-Three penile implants are available, the study said, ''for patients who fail with or refuse other forms of therapy.'' These include rods, either rigid or malleable, that are implanted in the penis to make the organ erect. Another device includes implanting in the penis a silicone sack that is inflated by a separate pump, causing an erection. All of these devices can develop side effects, including infection, the committee said. Additionally, the inflatable devices ''have a higher rate of failure requiring reoperation.''