The National Basketball Association's long and tiresome regular season finally is over, with 12 teams left for the serious business of what looks like a four-team race for the championship.

Last year's playoff finalists, Los Angeles and Philadelphia, have an excellent chance of meeting again for the title. Phoenix, which had the best record in the Western Conference, probably is the only team in that half of the field with the firepower to oust the Lakers. In the East, there are three legitimate contenders.

Philadelphia, Boston and Milwaukee are so evenly matched that it won't be easy for any of them to get to the best-of-seven final series. But the Celtics appear to have the easiest road. By beating the 76ers Sunday, they won the Atlantic Division title and tied the 76ers or the best record, 62-60, in the league.

Boston also gained a first-round bye and will play the winner of the Chicago-New York miniseries, which begins tonight in Madison Square Garden. The Bulls had the strongest finish of any team in the league, winning their last eight games.

Milwaukee, the Midwest Division champion, also got a first-round bye and will wait for the winner of the Philadelphia-Indiana two-or -three showdown. That should be the 76ers, which will set up an intriguing battle between them and the Bucks.

The 76ers had the better regular-season record (the Bucks were 60-20), so they would have the home court advantage if that best-of-seven semifinal comes about. But the Bucks have one of the most productive benches in the league with backup center Harvey Catchings and high scorers Junior Bridgeman and Brian Winters.

Their two best players, Marques Johnson and Sidney Moncrief, are extremely versatile. The Bucks also have a relatively healthy Bob Lanier to hold them together in the center. The 76ers still are Julius Erving's team, but he can be stopped by clubs like the Bucks.

The Celtics shouldn't have too much trouble doing away with either the Knicks or the Bulls in their semifinal and should be well rested for the physical conference finals.

Even though the Lakers finished three games behind the Suns in the West, they still are in fine shape because Magic Johnson is almost 100 percent recovered from the knee surgery that forced him to miss most of the season. The Lakers will have to get by Houston in the first round but, after Moses Malone, the Rockets are an ordinary team.

In the second round, the Lakers would play Central Division champion San Antonio. The Spurs are much better balanced, stronger rebounding and more defensive minded than San Antonio teams of the past. They still aren't ready to challenge the Lakers, though.

Portland finished the season with a rush and will play the Kansas City Kings in the other Western Conference miniseries. The Trail Blazers should advance and could give Phoenix trouble in the semifinals.