Julius (Dr. J) Erving returned home tonight with a magical all-around show, but it was Darryl Dawkins who brought down the curtain and assured the Philadelphia 76ers of a 123-115 playoff victory over the San Antonio Spurs at the Spectrum.

It was the 76ers' first victory over the Spurs in three tries in their best of-seven Eastern Conference semifinal series. The fourth game will be played here Sunday.

Erving was magnificient, scoring 39 points, grabbing nine rebounds and adding six assists, four steals and four blocked shots.

"It was time for us to do something," Erving said. "If we had gone three down, we would have been as good as dead. "Now we are only down, 2-1, and if we win Sunday it's a new series."

The Doctor carried the 76ers practically by himself for the first three quarters and then Dawkins entered the picture.

The 6-11 1/2 man-child scored 14 points and had eight rebounds in the fourth quarter and in one stretch scored 10 straight points to keep the Spurs at bay.

James Silas, who led San Antonio with 32 points, scored eight in the final five minutes of the third period to help the Spurs wipe out an 11-point Philadelphia lead and take an 88-87 advantage into the final 12 minutes.

Philadelphia came out firing for the last quarter, making its first nine shots and outscoring the Spurs, 18-6, to get its lead back to 11.

Then the Spurs, who were on the ropes much of the time, but always managed to get back into the game, regrouped. Silas scored five in a row. Mark Olberding and Coby Dietrick scored and Silas scored again.

All the 76ers could come up with during that stretch was one fast-break basket by Erving. With 3:52 to play, the Spurs had cut the lead to two - 107-105.

Then Dawkins took over. He sank two free throws and, after another Silas basket, slam-dunked a rebound. George Gervin scored at the other end, but Dawkins countered that with another slam-dunk after an offensive rebound.

Silas finally missed on San Antonio's next possession with Dawkins rebounding in heavy traffic.

At the 76ers' end, Dawkins scored on a finger-roll shot over Billy Paultz. Kenon missed for San Antonio and Dawkins rebounded again and was fouled by Olberding. He made two free throws and the 76ers had a 117-10. lead with 1:20 to play and the Spectrum crowd of 14,039 belonged to Dawkins.

Dawkins, who finished with 18 points, 10 rebounds and two blocked shots, said his inspired play in the fourth period was a direct result of "them beating up on me and me not getting the calls.

"The old Darryl Dawkins would have started fighting and probably got thrown out of the game," Dawkins said, "but that 's not me anymore. Instead of fighting, I controlled my temper and took it out on them a way that hurt them even more."

San Antonio's big guns, Gervin and Kenon, who averaged 58.5 points between them in the first two games, combined for only 46 tonight, with Kenon getting 22.

Gervin made 11 of 16 shots, but with super-quick 6-1 rookie guard Maurice Cheeks guarding him, Gervin didn't get the ball enough to get into the flow of the game. He also was in foul trouble much of the game.

The defense of Bobby Jones helped contain Kenon as he made only nine of 24 shots. He did add 15 rebounds and five assists.

"I think coming home really helped us," Erving said, "and it was a pretty even game until down the stretch. I think the difference was that we made them play catch-up basketball and we never let them build a lead."

Erving was effective tonight because he usually set up at the top of the key and the other 76ers stood aside and let him work.

San Antonio does not play very good individual defense and Allan Bristow, Olberding and Dietrick were no match for Erving. The Purs' team defense is suspect, also, so once Erving got by his man he usually had an unobstructed path to the basket. CAPTION: Picture 1, Elvin Hayes grabs first-quarter rebound from Hawk Jack Givens. Hayes scored 19 points, grabbed 14 rebounds in 89-77 victory. AP; Picture 2, Mark Olberding of San Antonio gets a forearm in the mouth for his efforts to stop Julius Erving on his way to a drunk. AP