Julius Erving scored 21 points and Caldwell Jones matched his single-game high for the season with 20, leading Philadelphia to a 100-93 victory over the Milwaukee Bucks today as the 76ers took a 3-1 lead in the teams' NBA playoff series.

Bobby Jones scored 10 of his 18 points in the fourth quarter for the 76ers, who can clinch the best-of-seven Eastern Conference semifinal series by winning Game 5 in Philadelphia Wednesday night.

The Bucks, beset by foul problems, were led by Marques Johnson with 23 points.

The Bucks started Alton Lister at forward in place of Johnson, who had four fouls, to start the second half, then inserted Johnson at guard when Brian Winters committed his fifth foul with 6:50 left in the third quarter. The 76ers, meanwhile, used a jumper by Caldwell Jones and a dunk by Erving to widen their seven-point halftime lead to 68-58 with 5:30 left in the period.

Johnson, taking the smaller Philadelphia guards inside, tipped in a rebound and banked in a short jumper to pull the Bucks to within 75-71 after three quarters.

A basket by Mickey Johnson cut the Bucks' deficit to 75-73 early in the fourth quarter, but the 76ers responded with eight straight points--a jumper and a drive by Bobby Jones, a jump shot by Maurice Cheeks and a dunk by Erving--to lead, 83-73, with 8:40 to play.

The 76ers lost center Darryl Dawkins on fouls moments later, but Bobby Jones' fourth basket of the quarter made it 88-78 with 5:50 left.

Milwaukee center Bob Lanier, who was scoreless in the first half and finished with only nine points, fouled out with 5:09 left as he crashed into Bobby Jones, who was posting near the 76er basket. Jones, who lay on the floor in pain for several minutes, eventually sank both free throws for a 12-point spread.

Marques Johnson, after scoring 13 points, went to the bench with his fourth foul 2:46 before halftime to further weaken the Bucks' depleted corps. Bucks' guards Quinn Buckner and Junior Bridgeman are sidelined for the duration with injuries.

"Quinn's and Junior's absence is really hurting us," said Marques Johnson. "They give us another dimension. Quinn's our quarterback and Junior's a great outside shot. They really left a gap. We tried to readjust but it has really been tough on us."

"It seemed like Milwaukee burned out a little," Erving said. "They had to play people a lot of minutes yesterday, and I think you could feel that late in the game today.

"There was a lot more holding and grabbing, and we got some breakaway situations that we wouldn't have had if they had rested players."