Three French physicians announced yesterday they had produced promising results in two AIDS patients treated with a drug normally used to prevent rejection of transplanted organs.

Skeptical American experts on acquired immune deficiency syndrome called the announcement extremely premature, however, cautioning that it was far too soon to tell if the French treatment would be of value in combating the deadly disease.

The highly publicized announcement was made at a Paris news conference by Drs. Jean-Marie Andrieu, Phillippe Even, and Alain Venet, researchers at the Laennec Hospital. News agency reports said they had given the drug cyclosporine to six patients over the past week and that two of them showed "dramatic" improvement almost immediately.

The French group said that the drug does not represent a cure, but claimed it produced improvements for the first time in the immune systems of the two patients with AIDS, apparently causing an unexpected upswing in crucial immune system cells that are destroyed by the AIDS virus.

Up until now, cyclosporine has been known for its ability to suppress the body's immune system and keep it from rejecting transplanted organs, almost the opposite usage to the French experiment. Marketed in the United States by Sandoz, Inc., it was commercially approved as a prescription drug for this purpose by the Food and Drug Administration in l983.

American researchers said they were willing to keep an open mind on the ultimate potential of the drug in AIDS cases, but sharply criticized the French doctors for publicizing findings that involved such a small number of patients over a so short a test period.

They also noted that the French findings had not been reviewed by others in the scientific community, a normal procedure before scientific experimentation receives wide sanction, and said the Laennec group was not known in this country for AIDS research studies.

A statement from France's Ministry of Social Affairs called the research "a hope for undeniable progress" that should be made public, The Associated Press reported.

But doctors contacted in the United States were concerned not only that the announcement would breed false hope in patients afflicted with a lethal disease that has no cure or treatment, but also that unduly favorable publicity could be harmful should others use cyclosporine, a highly toxic drug, before more is known.

"We would caution patients and physicians taking care of patients that it has not proven to be effective and most importantly, this particular drug can be extremely dangerous to individuals, particularly AIDS patients who are already immunosuppressed," said Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases.

"The risk you run, if the theory doesn't work, is that cyclosporine could be very damaging to a patient with AIDS," said Dr. Paul Volberding, a leading AIDS researcher at the University of California at San Francisco.

A spokesman for Sandoz said that the company was not aware of the French work and no such studies were being pursued in the United States.

The AP said the French doctors reported "dramatic biological results" in two patients, a 38-year-old reportedly near death after a two-year fight with AIDS and a woman suffering from a less severe illness known as AIDS-Related Complex, caused by the AIDS virus.

In the AIDS patient, they said that within two days there was an upswing in both in the number of T-4 cells, white blood cells that are attacked by the AIDS virus and the patient's condition. The T-4 cell count in the woman also rose dramatically, they said.

Fauci noted that other experimental efforts had produced fluctuations and temporary immune system improvements that proved of no long-term significance.

Volberding said the approach was of some scientific interest because of theories suggesting that AIDS may be a disease in which the "immune system self-destructs" after infection and cyclosporine might interfere with this process.