The National Basketball Association enters the final week of its regular season with four of its 12 playoff spots still undecided--two in the Eastern Conference and two in the Western.

The four division winners, plus the next four best teams in each conference, regardless of division, will make the playoffs, which will begin next week.

The division champions were decided long ago. In the Eastern Conference, the Philadelphia 76ers won the Atlantic Division and the Milwaukee Bucks the Central Division. In the Western Conference, the Los Angeles Lakers won the Pacific Division and San Antonio Spurs the Midwest Division. All four get first-round playoff byes.

The Boston Celtics and New Jersey Nets also have clinched playoff berths in the East. Washington, Atlanta and New York are vying for the remaining two spots.

In the West, the Phoenix Suns and Seattle SuperSonics are already in. The Portland Trail Blazers, Denver Nuggets and Kansas City Kings are battling for the last two spots.

In the East, New York and Atlanta (both 41-38) are a half-game ahead of Washington (40-38). Atlanta and New York have three games left and the Bullets four. The Knicks beat Indiana, 121-92, last night.

The Knicks, who have lost seven of 11, appear to have the easiest schedule. They will be at home against the Nets Wednesday, then will play at Detroit Friday and at Chicago Sunday.

The Bullets have the most difficult schedule of the three. Three of their games are on the road--at Philadelphia Wednesday, at Milwaukee Friday and at Cleveland Sunday. They play Detroit at home Saturday.

Atlanta will play host to the 76ers tonight and will play at Kansas City Wednesday before concluding the regular season at home against Milwaukee Saturday. The Hawks have a 1-9 record against those three teams. But Philadelphia's Moses Malone won't play against Atlanta because of tendinitis, although he is expected to face the Bullets.

The Bullets, having won 11 of 13, are the hottest team in the NBA, but still will need help to get into the playoffs. Since they lost the season series to both Atlanta and New York, they must finish at least one game ahead of one of them.

The sixth-place finisher will play the third-place finisher, most likely Boston, in the best-of-three first round. Number 4 plays No. 5.

The Lakers have clinched the best record in the Western Conference, but lost rookie forward James Worthy for the rest of the season when he fractured his leg in a game against Phoenix Sunday night. It's uncertain when Bob McAdoo, who had surgery on a toe three weeks ago, will return, and guard Norm Nixon hasn't played in a week because of tendinitis in a knee.

Portland has the fourth-best record in the conference, one game ahead of Kansas City and Denver in the race for the final two playoff spots.

The Kings have won eight of 10 and have games left with Chicago, Atlanta, Houston and Denver, the latter on the last day of the season. The Nuggets will play Houston, Utah and Dallas before the last-day showdown.

Portland must play Seattle, Golden State, San Diego and Los Angeles.

There is also an important race at the other end of the standings.

Indiana and Cleveland are battling for the worst record in the East. If the Pacers finish last, they will flip a coin with Houston, last in the West, for the first pick in the June 28 draft.

The Pacers' defeat last night may turn out to be more important to them than the victory was to the Knicks. Indiana moved within one defeat of clinching the worst record in the Eastern Conference and the chance for the top pick in the June 28 draft. Houston has the worst record in the West and would flip a coin with last-place Indiana for the first pick--almost certainly Virginia's Ralph Sampson.