The most severe forms of acne -- those resistant to all usual measures -- have responded dramatically to a new experimental treatment.

In tests at the National Institutes of Health in Bethesda, oral doses of a synthetic vitamin A derivative have cleared or almost cleared the badly marked faces of 38 longtime acne sufferers, aged 16 to 48.

They comprise 80 percent of the 47 treated by a National Cancer Institute headed by Dr. Gary L. Peck.

Peck and his associates report their results in today's issue of the New England Journal of Medicine. In an accompanying editorial, Dr. Peter Pochi of Boston University calls the NIH patients' recoveries "remarkable," and use of the vitamin compound "a potentially important advance."

Both the NIH team and Pochi warn that long-term trials are needed to learn whether the treatment has long-lasting results or harmful effects. This means it probably will take about three years before the drug can be made available to most doctors.

Peck yesterday warned teen-agers that the compound is not the same as ordinary vitamin A, and no one should take ordinary vitamin A for acne. Vitamin pills do contain small, safe amounts of vitamin A, but unlike the water-soluble vitamins that make up most vitamin pills, vitamin A in large doses can build up in the body and cause serious liver, bone, nerve and other damage.

The "cystic" and "conglobate" acne causing deep cysts and hard lumps makes up "about 2 percent of all acne," Peck estimated.

But 85 percent of teen-agers have acne at some point in adolesence. So the 2 percent with the severest types adds up to thousands of youngsters as well as adults in whom the disease persists.

Another vitamin A compound, vitamin A acid, has for some years been applied as a lotion to manage some acne.

The new synthetic -- known by the technical name 13-cis-retinoic acid -- was developed by chemists of the giant Hoffman-La Roche drug firm in Basle, Switzerland.

Its greatest successes have been in preventing cancer in experimental animals exposed to cancer-causing chemicals The National Cancer Institute is now beginning a trial of the drug in preventing the spread of early bladder cancer.

Doctors also tried the drug with mixed success in some other skin diseases.

In persistent acne, writes Pochi, they faced a disorder that causes "large, inflammatory," often tender and bleeding nodules on the face, back and chest, and "virtually inevitable" scarring and disfigurement.

The NIH team consists of Drs. Peck, Thomas Olsen, Frank Yoder, John Stauss, Donald Downing, Mangala Pandya, Danute Butkus and Jeanne Arnaud-Battandier.

They first treated 14 patients for four months apiece. The treatment completely cleared up the skins of 13, and removed 75 percent of the nodules and cysts from the 14th.

The good results have lasted for up to 20 months, causing the NIH group to hope that the patients will not need further treatment. The drug also has been used with 33 other patients with even worse acne, with complete clearing in 16 and nearly complete clearing in nine.

During the treatment, there have been some unpleasant effects, including skin redness, drying of nasal membranes and some eye irritation. "The drug turns off the oil glands, the sebaceous glands within the skin," Peck said. "But we are learning to get good results with just half the original dose."