The Boston Celtics and Philadelphia 76ers have played so well for so long that observers could be excused for believing that those teams meet each year for the right to represent the Eastern Conference in the NBA's championship series.

Since 1979, when the Washington Bullets lost in the title series to the Seattle SuperSonics, either the Celtics or the 76ers have made the finals. But when the teams play today at Boston Garden in the first game of a best-of-seven series, it will be the first time they've met in the postseason since 1982.

That year, the 76ers went ahead, 3-1, in games, lost the next two and had to return to Boston to decide it. In 1981, the 76ers had blown the series exactly the same way.

Minutes before the start of the deciding game in 1982, the 76ers retreated to their locker room. The reason wasn't to go over some last-second strategy, but to tell a few jokes. Sufficiently loosened up, Philadelphia went on to a 120-106 victory.

The main jokester in the locker room before that game was center Darryl Dawkins, who is now with the New Jersey Nets and has been replaced in Philadelphia by one Moses Malone. Malone, in his third year with the club, has yet to face Boston in the playoffs.

That is, as a member of the 76ers. When the Celtics won their 14th title in 1981, it was over the Houston Rockets, a team led by Malone. This season, the 76ers' 6-foot-11, 265-pound center averaged 26.5 points and 16 rebounds against the Celtics.

Another oddity: Dennis Johnson, acquired by the Celtics two years ago in part to work his considerable defensive magic upon Philadelphia's Andrew Toney, never has had a chance to do so in a playoff series. During the regular season, though, Toney averaged just under 14 points against Boston, low for him. Johnson averaged nearly 17 points against Philadelphia.

Boston, which succeeded Philadelphia last year as the league champion, had the best regular-season record in the NBA this year. Philadelphia was fourth overall after a surprising 13-12 finish in the regular season. But talk that the 76ers were ripe for an upset ended after they eliminated the Washington Bullets, 3-1, and had a 4-0 sweep of the Milwaukee Bucks, a team that many thought would prevent today's matchup from happening.

Instead there will be a Boston-Philadelphia series that has taken on the aspect of a command performance. "CBS couldn't ask for anything better," said Boston forward Cedric Maxwell after his team had eliminated the Detroit Pistons on Friday, 123-113. "They're at the top of their game. We have to raise ours a notch, but we'll definitely try to."

That might prove to be a problem early. The 76ers have been resting for a week. They eliminated the Bucks easily, while the Celtics were pushed by the Pistons. "It's hard to say that we'll be ready, either physically or emotionally," said Boston Coach K.C. Jones. "I'm sure that they'll do a lot of trapping against us and try to up the tempo. We'll just have to do the best we can."

It should be noted that following their four-game elimination of the Bullets in the first round, the 76ers had to travel the next day to Milwaukee to face the Bucks the following day. The final score: Philadelphia 127, Milwaukee 105.

"It'll be just one thing, the thugs against the thugs and anything can happen," said Maxwell, one of the few Celtics who is glad that his team is rushing right into the Philadelphia series.

The reason why is considerably less than altruistic. "I'm glad we're not getting any rest," he said. "If we had four or five days off, we'd practice, and I'd have to go to them."

The teams' often-bitter rivalry loses nothing during the regular season. This year, the teams each won three games at home.