Three underclassmen, Isiah Thomas of Indiana, Buck Williams of Maryland and Mark Aguirre of De Paul, most likely will be the first three players selected in Tuesday's National Basketball Association draft.

Though not necessarily in that order.

The Dallas Mavericks, with the first choice in the draft, had been expected to select Thomas, the clever sophomore point guard who led the Hosiers to the National championship this past season. But after Thomas met with Coach Dick Motta, General Manager Norm Sonju and owner Don Carter on Thursday, a team spokesman said the Mavericks are not yet totally committed to drafting Thomas.

"There's been a certain lack of enthusiasm since we got him in here," team spokesman Allen Stone said on Friday. "One of the big things we've been wrestling with is that nobody else (other NBA teams) seems excited about him. We don't have total peace of mind that we'll take him."

If Dallas does take Thomas, Detroit, drafting second, says it will take either Aguirre or Williams. New Jersey, picking third, will take whichever of the two is left.

Washington, with the 11th pick in the first round, still is considering its options but, General Manager Bob Ferry said, the Bullets are "assured of getting a good player.

"Our biggest decision between now and the day of the draft is whether to try to fill a void with someone who will help us win a few more games next year, or go for the best athlete available, no matter what his position, and strengthen ourselves that way," Ferry said.

A rebounding forward, a defensive guard and an outside shooter are the Bullets' top priorities. They also are looking for speed and quickness.

With the retirement of Wes Unseld after 13 seasons, the Bullets, long one of the league's most physical teams, will become more finesse-oriented, with a wide-open running game requiring runners and shooters.

The player the Bullets would like to get, 6-foot-6 guard Rolando Blackman of Kansas State, almost certainly will be gone before they draft. Ferry said he expects to be picking from among guards Frank Johnson of Wake Forest, Jeff Lamp of Virginia, Charles Bradley of Wyoming and Darnell Valentine of Kansas; center Herb Williams of Ohio State, and forwards Albert King of Maryland and Gene Banks of Duke.

Early handicapping of the draft has King going to the Nets, who also have the 10th pick of the first round, or to Kansas City with the seventh pick.

Ferry calls this draft "a blue-collar, or journeyman's, draft. There aren't many real stars you can build a team around, but there are a lot of players who can make it and last in the league. This could be the best draft in history in terms of new players making the rosters because of the added man to each team."

NBA teams will be allowed to carry 12 players instead of 11 on their rosters next season. For the Bullets, there is that opening, plus the uncertainty over the futures of free agents Mitch Kupchak, kevin Grevey and Bob Dandridge. Ferry said he wants to keep Kupchak and Grevey, but a decision on Dandridge hasn't been made.

The Bullets traded their second-round pick to Gold State for the rights to Jeff Ruland, but got a second-rounder (the 41st pick overall) from San Antonio for Dave Corzine. The Bullets also obtained the 48th pick overall, in the third round, from Detroit in the Larry Wright deal.

The top-rated center is 6-10 1/2 Steve Johnson of Oregon State. He is very effective on offense, particularly close to the basket, but isn't a polished defender or rebounder. He likely will be going to the Chicago Bulls on the fourth pick of the first round. North Carolina forward Al Wood, who might become a guard in the NBA, is expected to go to Seattle, which has the fifth pick.

New Jersey, with a new coach, Larry Brown, and a new arena, the Meadowlands, has three first-round picks: the third, 10th and 18th. Dallas, Detroit and Portland each have two first-round picks; Denver, Golden State, Houston, New York and San Antonio don't have any.

There are some interesting facets to this year's draft. Slick Watts, the bald-headed former Seattle SuperSonic who hasn't played in the NBA for two seasons, is responsible for the Sonics having the fifth pick and the Jazz the 13th. The Sonics unloaded Watts to New Orleans for a No. 1 pick before the Jazz moved to Salt Lake City. The Jazz shipped him off to Houston for a No. 1 pick, and the Rockets cut him.

Three of the top players in the draft, King, Bradley and Frank Johnson, have brothers playing in the NBA: Bernard King is with Golden State, Dudley Bradley is an Indiana Pacer and Eddie Johnson is a guard with Atlanta.