Thanks to some key injuries, slumps by a number of top teams and unexpected performances by other squads, the NBA suddenly is facing an exciting struggle for playoff spots over the final three weeks of the season.

Even mighty Portland, which once was threatening to set a league mark for most victories in a season, is struggling to avoid being passed by philadelphia for the best record in the league and the home-court advantage if the two meet in the playoffs.

Bill Walton, whose foot injury began the Trail Blazer's slump, might return this week, and his presence should be enough to save portland, which held a four-game edge over Philly after Saturday's contest.

If he is out much longer, though, the Trail Blazers' difficult remaining shedule, which includes road games at Philadelphia, Phoenix, Los Angeles and Seattle, makes them vulnerable.

Portland, Philadelphia, Denver and San Antonio have the championships of their respective divisions all but wrapped up, but otherwise the playoff picture in both conferences in muddled.

Eleven other teams are fighting for the remaining eight playoff berths, add one bullets.

In each conference, the six teams with the best records qualify.The division winners in each conference have first-round byes. The first-round pairings in each conference are the No. 3 teams vs. No. 6 and No. 4 against No. 5. The winnner of No. 3 vs. No. 4 plays No. 2 and the winner of No. 4 vs. No. 5 plays No. 1.

As of Saturday, teams qualifying in the West (in order) would be Portland, Denver, Phoenix, Seattle, Los Angeles and Milwaukee; in the East: Philadelphia, San Antonio, Washington, New York, Cleveland and Atlanta.

But in the West, Milwauke is only a game ahead of Chicago and Golden State for the sixth spot. And Phoenix, which once had the third-best record in the NBA, has slumped badly the last three weeks and could be passed for both Seattle and Los Angeles for the No. 3 placement before the end of the season.

In the East, Washington and New York likewise are staging a trussle for the No. 3 position and the resulting matchup with No. 6 in the playoff series. Cleveland, which had been strugling, ahs an outside chance of catching both the Knicks and Bullets.

But the Cavallers also have to watch their flank. Atlanta, which ranks as theNBA's surprise club, refuses to fold and is just a half-game behind Cleveland. And New Orleans in only one-half game behind Atlanta for the No. 6 spot.

Injuries could determine how well all of these eastern clubs do. Atlanta has been playing without leading scorer John Drew (sprained ankle) while Cleveland has been without Walt Frazier (bad toe). New Orleans has done remarkably well despite the absence of Pete Maravich (bad knee), who might try to play this week, either Tuesday against New Jersey or Wenesday against Washington.

The Bullets, of course, have been slowed by injuries since January, when Phil Chenier was lost with a back problem. As a result, the club is plagued by inconsistency and Coach Dick Motta has not been able to reestablish a substitution Pattern that was so successful earlier in the season.

In the rush to get Mitch Kupchak back in shape after his month layoff with a thumb operation Motta hardly has used Greg Ballard the last two weeks. And Larry Wright's right wrist is so sore he can't shoot, so Motta isn't playing him either. With Joe Pace in the coach's doghouse and Chenier sidelined, Washington has gone from being a 10-man team to seven-men club.

"This one could come back to haunt us," Motta said after Washington's 105-99 loss Friday to the Indiana Pacers in Capital Centre. "They know what they have to do, but only one guy (Mitch Kupchak) came to play."

This next stretch of games could prove crucial for Washington. The Bullets are pressing to play consistently and they need victories over the Bucks and BostonTuesday at home before leaving on a two-game swing to New Orleans and New Jersey.

Dandridgewho missed the Indianagame with a bruised thigh, is expected to play tonight. Kevin Grevely is hobbled by a bad ankle and Tom Henderson has a sore arm. Hayes his right have been troubling himm all season. Wright won't be at full strength for another week.

And the club said a month ago: "If we aren't careful, we'll be burned out by April, and that is the last thing we want to have happen."