When the Washington Bullets play the Milwaukee Bucks at the Mecca here Tuesday night, they'll be going against the latest NBA entry in the category of "Surprise Team of the Year."

Considered to be decimated by old age as well as a blockbuster trade that sent away three veterans, the Bucks nevertheless find themselves right where they finished the previous five seasons, atop their division standings. Winner of eight of its last 10 games, Milwaukee has astonished nearly everyone in the league with its play this season.

That includes the coach, Don Nelson. The NBA coach of the year for the 1982-83 season, Nelson may be on his way to another such honor, given his team's 22-13 record and three-game lead on the Detroit Pistons, considered by most observers a lock for the Central Division title.

"It's still very early, but it's been a special season for me so far," Nelson said. "Every good thing that could happen to a team has occurred here. We've been in most games and have found that to win we have to play as a team, which is what you want as a coach."

Team play and stifling defense have long been trademarks of the Bucks' success. Still, it was thought things would have to change this season following the retirement of center Bob Lanier and the trade of forwards Marques Johnson, Junior Bridgeman and Harvey Catchings to the Los Angeles Clippers for forward Terry Cummings and guards Craig Hodges and Ricky Pierce.

That deal was made only after Nelson decided against retirement, which he considered because of the stress that accompanied coming close but never advancing into the league finals.

After the trade was made, Nelson felt obligated to return, only because "I didn't want to stick someone with a poor team." That relatively negative attitude carried over into the team's preseason prospectus.

"You look at a team and try to think of a best/worst scenario," said Nelson. "Looking at the worst, we thought we'd be somewhere in the vicinity of the lottery (for No. 1 draft choice, involving the seven teams that don't make the playoffs), or maybe sneak into the seventh or eighth spot (in the 23-team association)."

As to the best projection, Nelson said, "We didn't really have one, definitely nothing like being good this far into the year. We had conceded winning the division."

Now another title is definitely within reach. Even in the framework of the team's all-around play, two players have stood out for the Bucks. Guard Sidney Moncrief, now an almost automatic choice for all-star honors, is having a banner season, averaging 22 points, six rebounds and five assists a game. But the most pleasant development for Nelson has been the work of Cummings. Although honored as NBA rookie of the year two seasons ago, Cummings had pretty much worn out his welcome with the Clippers, who accused him of selfish play.

Nelson does not tolerate that characteristic, and has not seen it in Cummings. Averaging 24 points and nine rebounds, the former De Paul athlete has surpassed the coach's expectations.

"He's definitely one of the special ones, a superstar," Nelson said. "I'd heard all the talk about him but to me the toughest thing was that he has such great skills that he was getting by, both offensively and defensively, doing things the wrong way.

"It's tough to tell someone, 'Yeah, you scored but it wasn't the way we want you to,' but he understood what we were talking about and has worked hard at it."

Dave DeBusschere, the New York Knicks' executive vice president, was said to be in meetings all day with his coaching staff and could not be reached for comment regarding his club's interest in Bullets guard Frank Johnson. New York sources disclosed that the two clubs held talks about the guard as early as last summer. The discussions reportedly stalled because the Bullets were asking a No. 1 draft choice . . . Bullets forward Cliff Robinson did not make the trip here, still disabled by a strained tendon in his right index finger. General Manager Bob Ferry said he did not know how long the injury will keep Robinson out. "They're just saying as soon as it feels good enough, he'll play," he said. Robinson has missed the last two games.