COLLEGE PARK, Md. (AP) _ Dr. Timothy Leary, the 1960s LSD guru, came to the campus where All America basketball player Len Bias died of a cocaine overdose, saying it is important to teach children to say no to drugs, alcohol and guns.

However, in a debate Wednesday at the University of Maryland, where counterculture heroes went up against anti-crime and law enforcement figures, he advocated freedom for adults to make their own decisions.

''To the adult human beings in America, the government can't possibly ... tell us who or what to put into our bodies,'' Leary said.

Leary and political activist Abbie Hoffman squared off in the debate against Peter Bensinger, former head of the federal Drug Enforcement Administration, and Curtis Sliwa, founder of the Guardian Angels.

Leary, dismissed from the Harvard University psychology department and jailed frequently during his days of drug experimentation, admitted, ''I am brain-damaged, there is no question about that.''

''At the altitudes and velocities I've traveled in the last 30 years, I know I have blown away several billion brain cells,'' he said.

Bensinger called mandatory drug testing as advocated by President Reagan useful to deterring widespread drug abuse, but Hoffman retorted, ''If you go with these drug tests, you are being led like blind sheep to drop your zipper for the Gipper.''

Sliwa, whose New York-based organization has branches in 25 cities, attacked Leary's and Hoffman's views of drugs, saying, ''How many other intelligent young creatures of the inner city, suburbs and rural areas that we have seen devastated, turned into Mr. Potato Heads, and you all are cheering that kind of genocide.''

Bias was found dead in June 1986.