Research suggesting a genetic and biological basis for homosexuality is changing the way the law and society look at gays and lesbians, according to a leading scientist in the field.

Dr. Simon LeVay, a prominent neuroscientist whose 1991 report revealed brain differences between gay and straight men, says that while such research is controversial, it is driving perceptions in a "useful direction."LeVay spoke at the University of Utah Sunday night at a forum sponsored by Family Fellowship and Parents, Family and Friends of Lesbians and Gays. About 200 people attended the lecture.

His address came just one week - and in sharp contrast - to the annual conference of Evergreen International, an organization that contends homosexuality is a developmental condition that can be "cured."

LeVay said the idea that a biological process is responsible for homosexuality was first advanced by a 19th century German scientist, though there was no evidence at the time to support the theory.

The biological theory was supplanted early in this century by the Freudian view of homosexuality as a consequence of defective parenting. Later "behaviorists" suggested that people start out as "clean slates" and could be steered toward or away from homosexuality by their environment, LeVay said.

In the 1950s, scientists began re-exploring the biological theory after finding evidence of a connection between sexual orientation and prenatal hormonal exposure. LeVay said later studies linked hormonal exposure to changes in an area of the brain called the hypothalamus.

His own research, which involved an examination of brain tissue from gay and straight men who had died of AIDS, found significant differences in a particular cluster of cells in the hypothalamus. The cluster was much smaller in gay men than in their heterosexual counterparts.

Born in Oxford, England, LeVay conducted his research at the Salk Institute for Biological Studies in San Diego. He has also been on the faculty of Harvard Medical School and is currently a freelance writer.

According to LeVay, research by other scientists suggests there is also genetic difference between homosexuals and heterosexuals. Some studies have shown that homosexuality tends to "run in families," he said.

LeVay said that while there is no public policy component to such research, "science is not conducted in a vacuum." Science is playing a role in public perception, and not everyone likes it, he said.

"One reaction I get is, `Don't do it. It's dangerous,' " LeVay said, referring to fears that the research might be used to persecute gays and lesbians.

He said there is also a fear that the research might lead to prenatal testing for homosexuality with the "very real possibility" of selective abortion. The scientists who developed a prenatal test to determine the sex of a child have already discovered to their horror that their technology is being used in some countries for the selective abortion of female fetuses, LeVay said.

However, the research has a "positive direction" as well, he said. Most recently, evidence of a biological basis for homosexuality has been introduced in a growing number of gay rights cases. LeVay himself has testified as an expert witness in several of those cases and says the science is beginning to "drive the law."

At the same time, the science is also influencing public perceptions, he added. He cited polls that show that people who believe there is a biological basis for homosexuality are more likely to be "gay friendly."