When last seen in public, Sunday afternoon, the Boston Celtics were boogeying on the basketball court to the sweet music of Jo Jo White's beat-the-buzzer jumper against the Philadelphia 76ers.

There was big Dave Cowens, wheeling squealing and dancing for joy as a national television audience looked on. "I was jst kind of happy," he said when it was over. "It's been a long time since I've done something like that."

And so, the Celtics apparently are back, playing with the proper blend of poise and emotion that brought all those championship banners to the hallowed rooftop at Boston Garden. And tonight, when game 2 of the best-of-seven Eastern Conference semifinal playoff series resumes in Philadelphia, they will have to have more of the same.

They are also going to have to do another number on the 76ers George McGinnis.Sunday the Celtics got McGinnies into early foul trouble and held them to only 11 shots and six points in 27 minutes.

"I had a bad game," McGinnis said yesterday. It's as simple as that. People have bad days, I had mine."

But coach Gene Shue is confident tht will not happen again. "I'm sure you'll see George explode and have some big offensive games," he said.

The Celtics had great success against McGinnis by sealing off his power move to the middle of the lane, forcing McGinnis to shoot turnaround, fall-away jump shots - hardly a high percentage shot manuever.

"In order for us to win, I don't have to score 30, but I do have to score some rebound some and concentrate on defense," McGinnis said. "Look at it this way. I scored only six points and we were still in it to the end."

While the 76ers were counting on Julius Erving (36 points) and Doug Collins (27) for their scoring, the Celtics have five men with 19 points or more.

Boston's victory at Philadelphia Sunday also took away Philadelphia's home-court advantage. "It's a shame," said Collins. "The whole season and then we lose it. Well, we'll just have to see what kind of backbone we have."

The Celtics have plenty of that, in addition to Cowen's intensity, Charley Scott's health, Jo Jo White's steady leadership and John Havlicek's potential for dramatic clutch play in the final minutes of any game. Says McGinnis, "I think they'll be the toughest playoff team we can play."

Boston forward Steve Kuberski injured his back during a scrimmage yesterday and will not play tonight.

There will be two other tough series being played elsewhere tonight when the West Conference semifinals begin.The Lakers take on Golden State in Los Angeles and Denver plays host to Portland.

Both the Lakers and Nuggets have had 10-days layoffs after winning their division titles and getting first-round byes.

"It's really difficult to say how it will affect us," said Laker coach Jerry West, whose teams srimmaged last week with the Houston Rockets in Salt Lake City to stay fresh. "I imagine we'll have stretches where we'll play sloppy ball. But we'll be ready to play."

"All I know is that Warriors have maginificent talent."

Denver assistant Frank Hamblen, who scouted Portland's mini-series against Chicago, said his team will have to stop the Blazers' running game.

"They run better than anybody I've seen all year," he said. "They send Walton and [Maurice] Lucas to the boards and their [TEXT OMMITED FROM SOURCES]

Denver will have its hands full containing Bill Walton and Co. The teams split their four regular-season games, but Walton missed both Blazzer losses because of leg injuries.[TEXT OMMITED FROM SOURCES] guards and small forward just take off. They shot over 50 per cent for the series, and that was mainly because they ended up with so many layups. And Walton is a great passer."