Rex Chapman caused quite a stir when he decided to give up his last two years of eligibility at Kentucky and make himself available for the NBA draft.

But Chapman, who was the Wildcats' standout sophomore guard, was just one of 12 players this year and 180 players since 1971 who took that leap. Going into this year's June 28 draft, 119 of those players had been drafted. Last yer, nine players declared themselves eligible and five were drafted.Only two - Seattle's Olden Polynice and Derrick McKey - were still in the league by year's end.

"A lot of these kids give up promising college careers thinking the NBA is their oyster, and it just doesn't turn out that way," said Harry Weltman, general manager of the New Jersey Nets.

The only other University of Kentucky player who left early was center Tom Payne, a 7-foot-2, 290-pound former Louisville Shawnee High School star who was the Wildcats' first black player.

Payne finished only one varsity season - in 1970-71 - before turning pro. He was drafted by the Atlanta Hawks and signed a $750,000 multi-year contract. But he played just one year for the Hawks before being sentenced to prison in connection with a series of rapes.

There are others whose lives have deteriorated after they left school early with NBA dreams.

"I'll tell you about a tragic case," said John Nash, general manager of the Philadelphia 76ers. "We took Vincent Askew (ho started three years at Memphis State) in the second round last year.

"First of all, Askew probably would have been a first-round pick if he had waited until this year. Then he suffered from being unable to adapt. He frittered away his opportunity, since he was unwilling to go out and bust his tail every day. One more year certainly would have helped him." Instead, Askew was waived.

"Whatever happens is going to happen," Chapman said. "I just want to do what I do best. There are going to be expectations wherever I go - I know that."

Nash said he doesn't think college players are ready for the NBA.

"There's such a huge jump from college to the Pan American or Olympic teams," he said. "Now take that another notch further, and you've got the NBA. Is a 21- or 20- or 19-year-old kid equipped to handle all the pressures that go along with that? I don't think so. Will it be fair to expect a kid like Chapman to step right in and be a star? I don't think so."

There are, however, plenty of success stories. Two all-stars who turned pro after their sophomore seasons are Los Angeles' Magic Johnson and Detroit's Isiah Thomas. Johnson left Michigan State in 1979 after winning a national title, while Thomas entered the draft in 1981 after leading Indiana to a national championship.

Chicago's Michael Jordan left North Carolina after his junior year in 1984. Julius Erving was a sophomore when he jumped to the American Basketball Association from the University of Massachusetts. Moses Malone jumped to the pros straight out of high school.

"I think it's up to the person who's making the decision to just look at what's best and decide if he's ready," Chapman said.