With George McGinnis playing hurt and Lloyd Free not playing at all, The Philadelphia 76ers will have to rely more than ever on Julius Erving against the Houston Rockets in their NBA semifinal plyoff series.

The Rockets showed Sunday that the Doctor can be stopped. Houston came back from a 17-point third-quater deficit Sunday by coping with Erving and won, 118-115, at the Spectrum in Philadelphia.

The sixth game of the best-of-seven series will be played tonight at the Summit in Houston. Philadelphia leads, three games to two.

McGinnis is hobbled by a groin pull and is not much of a factor on offence, or defense for that matter.

Free, the best 76er outside shooter, has a cracked rib and has missed the last two games of the e series. He will miss this one as well.

That means most of the scoring load will be on the 6-6 Erving. He scored 37 points Sunday, 27 in the first half. When the 76ers really needed the doctor in the latea going, the Rockets had just the antidote: a 7-foot center between Erving and the basket.

Erving becomes Dr. J on fast-break and open-court situations where he can innovate. But, as Rudy Tomjanovich, the man who has had to guard Erving most of this series, said, "When you get him into five-on-five situations, he's mortal."

That was never illustrated better than on Sunday.

"We were running and breaking and getting out fine for three quarters," Erving said. "We had trouble when we had to set up. We built the lead by running and lost it by not doing it."

With Free out, Erving played at guard Sunday and the Rockets could not match up with him.

Mike Newlin tried, but Erving dunked over him time after time.

The way to defend against Erving is to make him drive to the middle where there's help or make him shoot from outside.

The Rockets did both in the fourth quarter Sunday. The 76ers were getting the ball to Erving with Tomjanovich guarding him. Philadelphia was ahead, 105-100, with five minutes to play when Erving drove around Tomjanovich to the middle but found Moses Malone there to block his shot.

The next time he got the ball, Erving repeated the play but this time Kevin Kunnert was there to reject his shot.

The next two times he got the ball, Erving missed badly on jump shots and the Rockets had a 116-111 lead with a half-minute left in the game.

Erving is the series' leading scorer with a 27.2 average and he also leads the 76ers in assists, steals and blocked shots.

Even though the Tockets have a new life and will be playing before a sellout home crowd tonight, they know it is still an uphill struggle.

"Any dummy, including myself, knows the odds are against us," Houston coach Tom Nissalke said.

Nissalke was not happy with Newlin after the fourth game of the series and didn't plan to use him much on Sunday. But Calvin Murphy got into early foul trouble and Nissalke was forced to use Newlin, who responded with 19 points, three steals and four rebounds.

"He just went out and played," Nissalke said. "He didn't try to dominate the ball like he does sometimes."

If a seventh game is necessary, it will be played in Philadelphia Thursday. The final series against the Western Conference champion Portland Trail Blazers will begin Sunday.