The Washington Bullets will begin pursuit of another NBA championship by taking on the winner of this week's Houston-Atlanta best-of-three first round series.

For the last week, the Bullets had figured to meet either the Hawks or Rockets in the Eastern Conference best-of-seven semifinals. But the pairings were't locked in until yesterday, final day of the regular season.

When San Antonio, No. 2 team in the east, and Philadelphia, No. 3, both won their closeout games, that made it possible for either Atlanta or Houston to be paired against anyone else.

In the other Eastern Conference miniseries, Philadelphia will go against New Jersey, the winner meeting San Antonio in the semifinals.

The other major determination yesterday was the Midwest Division title winner Kansas City took its first-ever championship by beating Indiana while Denver, which had been tied with the Kings at the start of the day, lost to the 76ers.

Houston beat Washington last night at Capital Centre, so the Rockets took the home-court advantage in the short series against the Hawks.

Washington will begin its playoff trek either this Sunday or Tuesday, April 17, depending on whether the Atlanta-Houston matchup is decided in two or three games.

The Bullets split four games with both the Hawks and Rockets this season.

Kansas City and Seattle, which had the second-best record in the league, have the first-round byes in the Western Conference.

While they rest, the four remaining teams will be matched in what should be some interesting, highly competitive series.

Portland came on strong at the end of the schedule only to falter the last few days. The Trail Blazers will face Phoenix while Denver and Los Angeles meet in the other pairing.

Phoenix actually finished with a better record than Kansas City but the Kings automatically get a bye because they won the Midwest crown.

The weak-rebounding Suns had wanted to play Denver in the miniseries since the Nuggets don't have the kind of powerful front line used by Coach Jack Ramsay at Portland.

Los Angeles pulled a major upset Saturday night by beating the Trail Blazers in Portland, a most difficult accomplishment this season. That kept alive the Laker hopes of having the home-court advantage in the best-of-three against Denver, and Los Angeles won last night against Phoenix to secure that edge.

The Denver-Los Angeles winner will go against Seattle while Kansas City will meet either Phoenix or Portland. If the Suns win, they will have the home-court advantage versus the Kings. CAPTION: Chart, NBA Playoff Pairings