Two patients at the National Institutes of Health on Tuesday became the first to be treated for cancer using cells that have been genetically altered.

Dr. Steven A. Rosenberg, a National Cancer Institute physician, said the experimental technique was used on a 29-year-old woman and a 42-year-old man.He declined to identify the patients further but said "both tolerated the therapy well and are resting easily now."

Both patients are suffering from melanoma, the so-called "black mole" skin cancer. The disease is a particularly vicious form of skin cancer and neither patient has responded to other therapy. Untreated, their life expectancy was "limited," officials said.

Rosenberg said it will be several months before it is known of the treatment has any effects on the patients' tumors.

The cells that were injected into the patients had been altered by the insertion of a gene that causes the cells to produce tumor necrosis factor, or TNF, a powerful natural antitumor toxin.

The transfused cells are called tumor-infiltrating lymphocytes, or TIL, a type of white blood cells that naturally move into a cancer site and attack tumors. The cells were removed from the tumors, armed with the tumor necrosis factor gene and then cultured until they numbered in the billions. Then the cells were injected into the patients.

Rosenberg and his team have received approval by the Food and Drug Administration to treat up to 50 patients with the gene therapy technique. All of the patients are suffering from melanoma and are not expected to live.

The physician emphasized that the technique is still "highly experimental" and it may take many months and a number of patients before it is known if the gene therapy will successfully treat cancer.

Before it was approved, the experimental gene therapy proposal was considered by six different committees organized by the NIH.

Another form of gene therapy was approved Sept. 14 for the treatment of an extremely rare inherited immune system disorder called adenosine deaminase deficiency disease. That study's first patient, a 4-year-old girl, received a transfusion of her own white blood cells after a gene to correct the disorder had been inserted into the cells.

Rosenberg said that the progress of the 4-year-old is still being monitored, but no other patient has been treated for the immune system disorder.

Rosenberg has been using unaltered TIL cells to treat melanoma since 1987. The cells naturally migrate to tumors and have some cancer-fighting ability. But Rosenberg said they seemed to help only about half of the patients and the rest die of the disease.

To strengthen the treatment, Rosenberg and his team used genetic engineering techniques to insert into the TIL cells a gene that makes the tumor necrosis factor. The scientists also put into the cells a gene that is resistant to myacin antibiotics, for use as a marker in monitoring the treatment.