The Philadelphia 76ers, tired, sore and relieved, are thankful they've seen the last of the Milwaukee Bucks this season. Their reward for winning a grueling seven-game series was one day's rest before the National Basketball Association's Eastern Conference championship playoff with the Celtics begins tonight in Boston Garden.

The second game of this best-of-seven series will be played Wednesday night in Boston with Games 3 and 4 at the Spectrum in Philadelphia Friday and Sunday.

The Celtics haven't played since April 12, when they eliminated Chicago from the playoffs in four games.

"They've been beating up on each other all week, so I know they want some new meat," sid the Sixers' Julius Erving. "We'll give it to them and we're going to fight back."

"Boston is well rested, keyed up and ready to go," said Philadelphia Coach Billy Cunningham, "and we have to play three games in four days against the best teams in basketball. It isn't easy."

Cunningham gave his players yesterday off.

"I'm going to prepare for Boston by resting," Erving said. "Mentally, I can get ready in 10 to 20 minutes. I need all the time I can get to be ready physically, though."

The 76ers resorted to a special offense designed for Erving for much of Sunday's seventh game against the Bucks and Erving responded with 28 points in a 99-98 victory. He usually set up on the left side of the court with his four teammates on the opposite side, allowing him to go one on one with his defender.

That offense is much to Erving's liking. "It opens up my whole game," he said. "I had been playing a low post most of the series and it's tough to maneuver in there sometimes. Maybe we can use the same thing against the Celtics.I hope so."

The Celtics and 76ers had the best records in the league at 62-20 and split their regular-season games, 3-3. The Celtics have the home-court advantage in this series because of a better showing within the conference.

But the Celtics had the best record in the NBA last season and were eliminated, in five games, by Philadelphia in the 1980 Eastern finals.

"They're a better team than they were last year," said Philadelphia's Caldwell Jones. "The biggest change is that they have Robert Parish. He's the big shot-blocking center they needed."

Jones, who guarded the Bucks' Marques Johnson much of the Milwaukee series, will be assigned to Larry Bird against Boston.

"I'm going to have to be ready to chase him," Jones said. "He plays the whole court, so you can never relax on him. Everyone says he's slow, but he fakes so well that he either keeps you in the air or off balance."

In the other matchups, Erving will go against Cedric Maxwell, darryl Dawkins will be pitted against Parish and, in the back court, Maurice Cheeks will oppose Tiny Archibald and Lionel Hollins will be on Chris Ford.

The Boston Garden already is sold out for all four games scheduled there, while the 76ers aren't sure how many of their backers will be at the Spectrum. wOnly 6,704 showed up Sunday.

"We have more people than that on one of our charter flights," Erving said. "The fans don't win games for you, though, you have to do it yourself. It was a downer not to have more people in the seats, but I'm sure a lot more will be there when we play Boston. Half of them will; probably be rooting for the Celtics, though."