Fulfilling the ancient dream of preserving youthful skin, scientists reported yesterday that a relatively cheap drug used to treat acne can reverse wrinkles and the other signs of aging caused by the sun..

The treatment, using a topical cream called tretinoin, softened rough skin, faded age spots and enriched the complexions of almost every patient who tried it, according to a paper published in today's issue of The Journal of the American Medical Association.

"The article suggests that a new age has dawned," wrote Dr. Barbara A. Gilchrest, of the Boston University School of Medicine, in an accompanying editorial. "An enthusiastic reception for this report is assured."

Dermatologists have for some time suspected that Retin-A, the drug's trade name, helps erase wrinkles caused by the sun. And many have prescribed it for that purpose. But today's report is the first to provide persuasive scientific evidence in support of those claims.

"The effects were far more dramatic than anything I had anticipated," said Dr. John J. Voorhees, chairman of the dermatology department at the University of Michigan Medical School and the chief investigator in the study. "Obviously, the implications are pretty big."

The cosmetics industry long ago turned Ponce de Leon's dream of attaining eternal youth into a billion-dollar industry. But while generations of cosmetic adventurers have tried to reverse the aging process, none has succeeded.

In the Voorhees study, 30 patients ranging in age from 35 to 70 rubbed Retin-A on one forearm daily and a cream containing no medication on the other. Half the subjects also tested the drug on their faces. None of them knew which cream contained the drug.

Every patient showed significant reversal of skin damage caused by the sun on the tretinoin-treated forearms but not on the others, according to the report. In addition, all but one of the patients who rubbed tretinoin on their face showed improvement there while none of the others did.

More than 90 percent of the patients experienced temporary inflammation of the skin. "It usually goes away if you stop the drug for a day or two," Voorhees said. "But it's very important to note that this study was done under controlled conditions using high concentrations of cream."

Voorhees said anybody who wants to use the drug should first consult a dermatologist.

Although the study lasted for 16 weeks, Voorhees said yesterday that many of the patients have continued to use the drug for more than a year.

The research was designed to look at the effects of sun on the skin, the cause of nearly all wrinkling, but the scientists also found that the treatment appeared to improve wrinkles caused solely by aging as well.

The researchers found that 30 percent of tretinoin-treated forearms showed slight improvement, 40 percent showed definite improvement and 30 percent showed great improvement.

There is no way of knowing whether continued use after the initial four months will have an improved clinical effect. Voorhees said he has had trouble getting volunteers to stop using the drug so he can make comparisons.

Because dermatologists have used tretinoin for more than 15 years in treating acne, its side effects have been studied extensively. In the Michigan trial, skin problems caused by the drug lasted two weeks to three months, according to the report. Forty patients entered the study. Three left because of severe inflammation and seven for personal resons unrelated to the treatment.

Retin-A is technically available only for treating acne. Its maker, Ortho Pharmaceutical Corp., which paid for part of the Michigan study, is seeking approval to market it for wider use. A 20-gram tube of the cream costs about $20 at most Washington-area pharmacies. And doctors said yesterday that amount could last at least two months.

Once a drug is approved by the Food and Drug Administration for one use doctors are free to prescribe it in other ways as well. Many dermatologisits have already begun giving their patients the drug for sun-damaged skin.

"Many of my patients are aware of it. And I have prescribed the drug for wrinkles," said Dr. Philip G. Prioleau, director of dermatologic surgery at New York Hospital-Cornell Medical Center. "For acne it has proven extremely effective. It could even turn out to help prevent skin cancer caused by the sun," he added.

The Michigan group also found tentative evidence that the drug improved premalignant cells in the skin.

Use of the drug has been shown to produce a wide variety of metabolic changes within skin cells, causing them to multiply faster and to manufacture proteins in different proportions.

The outer layer of the skin, called the epidermis, becomes thinner as it ages or is damaged by the sun. That causes fine wrinkles just below the surface where blood vessels supplying the skin have been reduced in number over time.

As the aging process intensifies, collagen, which maintains the shape and elasticity of the skin, also diminishes.

Trentinoin stimulates the collagen and nearly triples the thickness of the epidermis. That makes the skin stronger and more wrinkle resistant.