A study indicates a French drug significantly - and safely - reduces opportunistic infections in patients infected with the AIDS virus, scientists reported Wednesday.

The study of 389 patients at eight U.S. medical centers was the biggest investigation ever of ditiocarb, or diethyldithyocarbamate.The researchers found a 56 percent reduction in opportunistic infections, or diseases that take advantage of an AIDS patient's damaged immune system.

Opportunistic infections are often the cause of death in AIDS victims. They include a rare form of pneumonia and various fungal infections.

"There is a significant effect on opportunistic infection, and the drug seemed to be relatively non-toxic and safe to give," said the Arizona Cancer Center's Dr. Evan M. Hersh, who headed the study.

The findings were reported in the Journal of the American Medical Association.

Ditiocarb was developed by Pasteur Merieux Serume et Vaccine of France, which is conducting a 1,600-patient study in France using the drug with and without the AIDS drug AZT. AZT is used to delay the progression of the disease.

Researchers aren't sure how ditiocarb works, Hersh said.

The patients were studied for 24 weeks each, with 191 receiving ditiocarb and 196 a placebo. Two patients did not receive therapy for most of the study. Neither patients nor doctors knew who received the drug and who got a placebo.

Excluding the two, the study group consisted of 375 men and 12 women, with 278 having some symptoms of AIDS and 109 having full-blown AIDS. Patients ranged in age from 18 to 68.

Of the 31 patients who developed a new opportunistic infection, only 10 had received the drug.

Among patients with full-blown AIDS, seven taking the placebo developed a new infection, versus only one on ditiocarb.

Eight deaths occurred in each group, the researchers said.

"I'm not sure the numbers are large enough to give us any hint about the effect on survival, and that's why we feel another study is indicated," said Hersh, who is chief of hematology and oncology at the cancer center.