It's final four time in the National Basketball Association--even though the champion won't be decided for another month.

The four remaining teams--the defending champion Los Angeles Lakers and San Antonio Spurs in the West, and last year's runners-up, the Philadelphia 76ers, and Milwaukee Bucks in the East--were the four division winners and the four top seeds.

If there is a surprise, it's that the Bucks handled the Boston Celtics so easily in the conference semifinals.

The Bucks and 76ers begin their best-of-seven series today at the Spectrum (WDVM-TV-9, 1 p.m.) and the Spurs and Lakers play the first game of their series at the Forum (WDVM-TV-9, 3:30).

All four survivors are fun-to-watch teams and have almost an equal number of the league's best athletes.

Eleven players who were in this year's all-star game are on these teams.

Of the game's top do-everything stars, only Larry Bird is a conspicuous absentee. The others, like George Gervin, Magic Johnson, Marques Johnson, Sidney Moncrief and Julius Erving, are here.

But the keys to each series are the centers, and they are four of the best ever to play the game.

Can Artis Gilmore negate Kareem Abdul-Jabbar and can creaky-kneed Bob Lanier offset the dominance of Moses Malone?

"I don't like playing Moses," said Lanier, who outplayed Boston's Robert Parish in the Bucks' four-game sweep of the Celtics. "He runs so well and is one tough young man.

"It's going to be a job, but this is the furthest I've ever gone in the playoffs and I'm not ready to get off the cloud, yet," said Lanier.

"Bob is big and strong enough to guard Moses, but we're still going to help him," said Moncrief. "I don't think Moses can stop Bob by himself, either, though."

Malone averaged 31.3 points and 15.5 rebounds and played 41 minutes a game in the 4-0 sweep of the New York Knicks.

He said Lanier has given him trouble in the past, "but I'm going to do the same things I always do--shoot the jumper and get the boards. That's my job."

Lanier averaged 28 minutes a game and 12.8 points and 7.3 assists against the Celtics. EASTERN CONFERENCE

76ers-Bucks

The 76ers won five of the six regular-season meetings, but the Bucks were injured all season. Lanier played in only two of those games and Moncrief played in four. Malone averaged 26.3 points and 15.3 rebounds and played in all six games.

The Bucks' stars are Moncrief and Marques Johnson, and they often play a two-man game that the Celtics had considerable difficulty stopping.

Moncrief averaged 23.3 points, 6.5 rebounds and four assists against the Celtics in the conference semifinal, and Johnson averaged 22.8 points, 8.3 rebounds and four assists.

Injuries could play a major part in this postseason. As long as Lanier stays healthy, the Bucks can win, but if he goes down, so do the Bucks. He played in all four games in the Boston series with little discomfort. He had his knee drained Tuesday and said he felt as good as he has all season. Dave Cowens, who missed the Boston series with a bad knee, is expected to be available for limited action.

The most seriously hurt of the 76ers is Andrew Toney. He has a deep thigh bruise that caused him to miss one game of the New York series. He averaged only eight points in the three games in which he played. Cleamon Johnson, who pulled a hamstring against the Knicks, and Maurice Cheeks, who sprained his ankle, have healed. WESTERN CONFERENCE

Lakers-Spurs

The Lakers swept the Spurs in the conference final last year, but they had Bob McAdoo then and the Spurs didn't have Gilmore. The Spurs won four of the five regular-season meetings and are healthy and hungry going into this one, as evidenced by their record-setting series against the Denver Nuggets.

San Antonio averaged 132.8 points, eight points better than the NBA record for a five-game playoff. The Spurs had six players average in double figures and three at 20 or more: Gervin (28.2), Johnny Moore (27.2) and Gene Banks (20).

Moore also set a five-game playoff record with 71 assists and had a record 20 in one game.

Abdul-Jabbar was the big man in the Lakers' semifinal series against the Portland Trail Blazers, won in five games. He averaged 30.8 points and eight rebounds.

The Spurs are healthy, but the Lakers are down to six proven players. McAdoo is slow recovering from foot surgery and is questionable, and James Worthy is out the rest of the season with a broken leg.