When a coach starts fooling around with his lineup during playoff time, it is usually a sign of desperation and panic.

That is precisely the state Philadelphia Coach Billy Cunningham was in Thursday when his 76ers took the floor against the San Antonio Spurs in San Antonio. The 76ers were trailing, three games to one, in their best-of-seven NBA Eastern Conference semifinal playoff series.

So Cunningham moved his best player, Julius Erving, to guard, benched Henry Bibby and put Darryl Dawkins in the lineup.

The 76ers were a different team with that massive lineup. They buried the surprised Spurs by 23 points and changed the complexion of the series.

San Antonio Coach Doug Moe said now that he has seen that big Philadelphia lineup and what it can do, he doesn't know what he'll come up with to counter it in game six today in Philadelphia (WDVM-TV-9 at 1:30 p.m.). If the 76ers win, the seventh game will be played Wednesday in San Antonio.

The series winner then meets the survivor of the Washington-Atlanta battle in a best-of-seven series for the Eastern Conference championship.

The Western Conference finalists were set Friday night when Phoenix beat Kansas City, 120-99, in the fifth game of their series. Seattle gained the Western Conference final Wednesday after eliminating the Los Angeles Lakers,also in five games.

The Phoenix-Seattle series begins in Seattle Tuesday night.

The move of Erving to guard for the 76ers was inevitable. He proved he could play the position at the NBA All-Star Game in February.

"I never should have played him at guard," said Washington Bullets Coach Dick Motta, who coached the East All-Stars, "I put the idea in their heads."

Erving, who had 15 points in the fourth game of the semifinals as a forward in Philadelphia, responded with 32 points as a guard in San Antonio.

Playing Erving at guard does a number of things to improve the 76ers. It puts their most physical player. Dawkins, in the starting lineup; it puts their best player, Erving, in the position where he can do the most and it takes their least effective starter, Bibby, out of the lineup.

Surprisingly, Cunningham did not put the 6-foot-6 Erving on 6-7 George Gervin, the Spurs' high scoring guard. Instead, he left 6-1 rookie Mauriee Cheeks on him, deciding to play Genvin with quickness instead of size-Erving was matched with the other San Antonio guard, 6-3 James Silas.

Silas likes to back into the basket and then use his strength to get off his shot. Erving wouldn't let him do that. Gervin had been averaging 29 points a game and Silas 23. In Thursday's game they scored 13 and 19 points, respectively.

Phoenix got 32 points from guard Paul Westphal in Friday's victory. He scored.4 in the first half. Walter Davis and Mike Bratz had 18 points apiece.

The Kings, who were down 70-46 at the half. got 21 points from Otis Birdsong but only three from Phil Ford. The Kings made only 5 of 28 field-goal tries in the second quarter when the Suns broke open the game.

"The best team who. There's no doubt about that." said Kansas City Coach Cotton Fitzsimmons. "We got baptized."