Buck Williams, Maryland's standout junior center, will pass up his final year of college eligibility to play in the National Basketball Association, it was learned last night.

Williams decided to declare himself elibible for the June 9 draft minutes before the midnight deadline after receiving guarantees from the Detroit Pistons and the New Jersey Nets that they would make him their No. 1 draft pick. Detroit will draft first or second and New Jersey will draft third.

Williams' decision came on the same day that Virginia's 7-foot-4 sophomore Ralph Sampson decided to turn down the pro ranks to remain at Virginia for another season. Two other star players, De Paul junior Mark Aguirre and Indiana sophomore Isiah Thomas also decided to turn pro. Georgia sophomore Dominique Wilkins decided at the last moment to remain with the Bulldogs.

The Dallas club refused to talk about specific sums of money with Falk, who then spoke with officials from Detroit and New Jersey. The Pistons will flip a coin with Dallas for the first pick on Thursday. If they win the flip, they are expected to draft Thomas. Because of that and Dallas' refusal to guarantee it would pick Williams, a guarantee from New Jersey, picking third, was needed before Williams would agree to make the move.

Negotiations with the three temas dragged on until just before midnight. A letter to the NBA office declaring Williams eligible for the draft was postmarked shortly before midnight.

"I don't think Buck realized just how highly he was thought of until he tested the market," said one NBA general manager. "He wasn't coming out without a guarantee. Once he had it, though, it was inevitable. I think his attorney was pushing him to make the move."

Williams' departure means that Maryland will lose its top four scorers from this season's 21-10 team. Maryland Coach Lefty Driesell, who spent the day waiting for a phone call from Falk, said last night, "I really don't want to talk about it right now. I just really don't have any comment."

Sources in Dallas say Maverick Coach Dick Motta has said he would like to add Williams to his lineup.

Sampson, a 7-foot-4 sophomore with two more years of college eligibility, originally planned to announce his decision by way of a taped message today. But early yesterday, he called Doug Elgin, Virginia sports information director, and Todd Turner, director of sports promotion, and informed them he planned to return to Virginia "for at least one more year."

In explaining his sudden change of plans, Sampson said he'd "been through a lot of stuff this week, strange and unnecessary stuff, and I was tired of waiting.

"It's been a tough week and I wanted to get this straightened out," Sampson's taped response said. "I hope I won't have to go through it in the near future, like people grabbing me on the arm and following me to class. Hopefully other players won't have to go through that.

"I had made up my mind (Friday night) and I figured that I would go ahead and come out with it instead of Sunday afternoon at 12. I just made up my mind I would stay at Virginia for another year."

Sampson, who was not available for comment yesterday, had met with and the Mavericks and Pistons.

Both clubs had said they would definitely pick Sampson and reportedly were prepared to offer him as much as $1 million annually.

In an interview on CBS Sports yesterday, Sampson said the Pistons had initially offered a package that would total $3.85 million over six years, then had raised the offer. Sampson later confirmed that offer to be $1 million a year.

Sampson did not mention the Dallas offer and he also indicated he would use the same method next season in deciding whether to turn pro after his junior year.

"The NBA draft comes every year and the hardship comes every year," Sampson said. "You have to look at what's there. I have been saying that I was going to stay anyway. You have to look at the situation you are being dealt and evaluate it.

"I've been here two years and I really don't have to make a decision. I have a four-year scholarship and usually people go four years. I figured I was winning here an I would just stay with a winning situation."

Dallas spokesman Allen Stone said, "We felt there was never than a 50-50 chance he would (turn professional). If he's 19 and he's not ready to come out of college, he shouldn't come."

NBA Commissioner Larry O'Brien said in a statement: "I have no doubt Mr. Sampson eventually will play in our league and it may well be that another year or two of intercollegiate basketball will enable him to further develop his game to the point where he would be better prepared for the level of competition in the NBA.

"I think it is unfortunate that Mr. Sampson and his coach (Terry Holland) insisted on entering into premature financial discussions with NBA clubs, and the NBA Board of Governors will be studying ways in which the NBA might be able to avoid this type of activity in the future."

The one person who felt all along Sampson would not leave was Holland.

"There was never any doubt in my mind he wanted to stay. I do think that he at least had to listen and I encouraged him to do that," Holland said. "He's been very solid in that decision. Probably, I've been at fault in terms of creating indecision in other people's minds inthat I've asked him to consider all options, to make sure he was doing the best thing for himself. I think that's exactly what he's done."

"The pro people said, 'We've got to talk to you (Sampson),' and he sat down and listened. I think when the Detroit people left, they knew for sure he was not seriously considering leaving unless they could come up with something new he hadn't heard or already considered. I think he feels that it's just not time for him to go and he definitely needs another year in college basketball."

Sampson had told Holland last fall that he was staying at Virginia and had told all of the prospects who visited the campus that he would be there for his junior year. Thus Holland didn't recruit any centers.

"He's never wavered in his resolution to keep attending the University of Virginia," Holland said. He's consistently gone to class, he's registered for class and made plans on where he's going to live next year. He's been real solid about this, above board the whole way. In fact, I'm the one who suggested he wait until Sunday to make the announcement to give himself breathing room and make sure he was doing the best thing."

Thomas, meanwhile, becomes the first Indiana player to leave school early to turn professional in the 10 years Bobby Knight has been coach. In a radio interview, Thomas said the reasons for turning pro were "my family, myself . . . and I can always go back to school and get an education, but I can't always make a million dollars."

In Athens, Ga., Wilkins said the Detroit Pistons had proposed a $1.28 million offer for four years, but that was not enough to make him declare himself for the draft.