Drug-related AIDS cases are increasingly linked to cocaine rather than heroin, and crack users who trade sex for drugs may be spreading the epidemic further, a researcher said Wednesday.

Drug-related AIDS also is spreading to parts of the developing world where illicit drug shipments originate, said Don Des Jarlais of the New York State Division of Substance Abuse Services in New York City. He spoke at the Fourth International Conference on AIDS.The reason for the growing link between AIDS and cocaine injection may be partly due to the frequency with which cocaine users inject themselves, Des Jarlais said.

Heroin users may inject themselves three or four times per day, Des Jarlais said. But cocaine users may inject themselves as often as every 15 minutes until their cocaine supply is exhausted, he said.

"That can lead to almost continuous sharing of drug injection equipment and a much greater likelihood of viral transmission," he said.

The AIDS virus attacks the body's immune system, leaving victims susceptible to a wide variety of infections and cancers. It is most often transmitted through sexual contact.

Various reports at the AIDS conference have identified the sharing of needles by drug abusers as one of the most rapidly growing components of the AIDS epidemic.

The disease also can be spread in transfusions of tainted blood or blood products and from mother to child at or before birth.

Crack users do not inject the drug, but the trading of sex for drugs could be further spreading AIDS infection among the drug-abusing population, Des Jarlais said.

The spread of AIDS among cocaine abusers, which Des Jarlais has observed in New York City and San Francisco, is also of concern because of the difficulty of treating cocaine addiction, Des Jarlais said.

"We currently lack any large-scale treatment for cocaine dependence," he said. Heroin addiction can be controlled by substituting methadone for the drug, but there is no such substitute for cocaine.

Des Jarlais said the spread of AIDS among drug abusers appears to be slowing. In San Francisco, 15 percent to 20 percent of cocaine and heroin abusers have been infected with the virus, but that figure has not increased for about 18 months, he said.

In New York City, 55 percent to 60 percent of the drug abusers are infected, and that figure has been stable for about three years, he said.

"We have seen substantial behavior change in a variety of cities," he said.

In a separate report, researchers said Tuesday that proportion of drug-related AIDS cases among Puerto Ricans in the United States is more than five times the rate among other Hispanic-Americans.

Hispanics make up just 6 percent of the population but have 14.5 percent of the country's AIDS cases. As of June 6, the U.S. Centers for Disease Control had reports of 9,362 cases in Hispanics, out of a total of 64,506 cases.

Richard Selik of the Centers for Disease Control said 38.6 percent of the AIDS cases among Puerto Ricans in the 50 states occur among drug abusers or their heterosexual partners.

In the largest study yet done of AIDS transmission to newborns, European researchers who have followed 219 infants of infected mothers for up to two years said it appears that 25 percent to 30 percent of infants born to infected mothers will be infected themselves.

Of the infected infants, 40 percent will go on to develop AIDS or a related illness, said the study's director, Dr. Catherine Peckham of London's Institute of Child Health.