Call them a sleeper. Call them a surprise. Call them anything you want to. To Washington Diplomat Coach Gordon Bradley there is one word to describe the Dallas Tornado; dangerous.

"They could be the most dangerous team we'll face all season," Bradley said of Sunday's 2:30 p.m. opponent at RFK Stadium. "They've gone out and bought half the Bundesligia."

The Bundesligia is West Germany's version of the NBA, the NFL or the NHL. Soccer in West Germany is equivalent to basketball in the U.S. or hockey in Canada in popularity.

After missing the NASL playoffs last season, the Tornado purchased five players from the Bundesligia. The best of the bunch was striker Klaus Topmoller, who immediately challenged Giorgio Chinaglia of the Cosmos to a $5,000 bet on who would score more goals this season.

Topmoller has had one goal in the Tornado's first three games, but that has been enough. Dallas is 3-0, the best record in the NASL going into Sunday's game with the 1-2 Diplomats.

Topmoller also has been getting plenty of help from surprising sources. One is Danish midfielder Flemming Lund, always known as a player with a very high work rate but never known as a scorer. Lund didn't score a goal in 26 games last season.

After a season-opening 2-1 win against Atlanta, Tornado Coach Al Miller pulled Lund over in practice and told him his lack of offensive aggressiveness hurt the team.

Lund responded with two goals the last two weeks, including the winner in a 1-0 overtime victory against Houston last Saturday.

There are also three starting Americans who can hardly be considered tokens. Defender Tony Bellinger, who probably will mark John Cruyff Sunday, is a four-year starter at age 23, Midfielder Steve Pecher, in his third year as a starter, is 22. They are the team "veterans," in terms of time spend with the Tornado.

Finally, there is goalie Billy Phillips, 22, a graduate of Adelphi University in Garden City, N.Y. Thrust into the starting role this season, he has responded with two shutouts and a 0.33 goals-against average in the three games. The play of the young Americans allows Miller, one of two native Americans coaching in the league, to smile more broadly.

"They've all played well for us so far," Miller said. "We're playing well but I think as the season progresses and we get to know each other, we'll be that much better."

That sounds a lot like Bradley, who also has several new, talented players he is working into his club. There is one major difference: the Tornado has played its first three games at home while the Dips played two of three on the road.

That fact concerns Miller. His team has played three games on artificial turf in Texas Stadium and now faces its first game on grass. The Tornado will play 24 of 32 games on artificial turf, the Dips just seven of 32.

The Tornado was one of the original NASL teams 14 years ago and its past claim to fame was Kyle Rote Jr. Rote no longer plays soccer but the Tornado does. And, as Bradley put it, "You may not know much about them now but by the end of the season everyone will. They can play the game."

Dip Striker Bobby Stokes, who injured a calf muscle Wednesday, is a doubtful starter Sunday. If he can't go, Kenneth Mokgojoa will start up front with Alan Green . . . The Dips, who left Joe Horvath out of the 1980 media guide, sent out a bio after his play last week.