A new era of pizazz offense dawned yesterday at RFK Stadium and not a moment too soon for the Redskins as they managed a thrill-a-minute 35-39 victory over the Philadelphia Eagles.

The Redskins prevailed by the margin of a razzle-dazzle 37-yard touch down pass from Joe Thiesmann to Danny Buggs on a play that started out as a John Riggins run off tackle.

That touchdown, 26 seconds into the final quarter, on a play the Redskins put into their offense just last Tuesday, gave Washington a seemingly safe 19-point advantage. But the Redskins nearly handed the game right back to an Eagle team that never gave up, with three costly turnovers in the final period.

Only when Philadelphia running back Cleveland Franklin dropped a pass at the Washington 25-yard line with no time left on the clock could the sellout crowd of 54,380 and the Redskins themselves - breathe easily for the first time since the Eagles started making their four-period comeback.

On a day when the Redskin cheerleaders bared backs and bellybuttons with some eye-popping new costumes, the Redskins also took the wraps off an offense that had been mostly moribund since the team assembled in training camp in July.

Theismann threw three touchdown passes, two to tight end Jean Fugett and ran for a score. He completed 14 of 29 passes for 226 yards as the Redskins had their most prolific point-scoring afternoon since the 13th game of the 1976 season.

It also made the Redskins 2-0 in this young season, which continues Sunday with a trip to St. Louis for a 1 p.m. game with the Cardinals.

Rookie running back Tony Green provided the other touchdown with an 80-yard run on a punt return that began with him dropping the football and succeeded after a clip that was never called.

But while Theismann and Co. were posting all those points, the Redskin defense was no match for second-year Philadelphia tailback Wilbert Montgomery, who blasted across the goal line three times on runs of 34, eight and five yards and caught a 10-yard touchdown pass from Eagle quarterback Ron Jaworski.

Montgomery had a fifth touchdown nullified early in the fourth quarter when he ran five yards off tackle, only to have the play called back when offensive guard Woody Peoples was caught holding.

Two plays later, Redskin middle linebacker Mike Curtis intercepted a Jawtrski pass in the end zone to kill that threat. But the Eagles kept coming.

"They just kept the heat on the whole thing," said a relieved Redskin Coach Jack Pardee. "I knew they would. You don't like to play the Eagles with a two- or three-point lead. But that's the NFL. No lead is ever safe."

Certainly no lead was safe the way the Redskins were playing giveaway with the football in those final, frantic minutes.

Theismann had a sideline pass tipped at the line of scrimmage and Eagle defensive end Carl Hairston intercepted the batted ball and returned it 12 yards to the Redskin 16.

Five plays later, Montgomery carried off tackle from five yards out to cut the Redskin lead to 35-30. Then the fun really began.

Redskin tailback Mike Thomas, who fumbled earlier in the period, could not hold on to a low pitchout at his 40-yard line and Eagle nose guard Charlie Johnson recovered at the Redskin 34.

Jaworski was unable to pick up a first down and, after Redskin defensive end Karl Lorch sacked him for a 10-yard loss, the Eagles were forced to punt. Rick Engles lofted a high kick that landed at the five and was downed by Billy Campfield at the Washington one.

Pardee said later probab ly would have accepted a safety at that point had the Redskins not been able to get the ball past the five-yard line.

But that decision never had to be made because Thomas got four tough yards on first down and Riggins went off tackle for 11 and a vital first down on the next play at the two-minute mark.

"I just read the guard's block and when their end came down at me I bounced it off him and got free," Riggins said. "I probably should have gotten more yards, but at that point . . . I just figured I was better off getting the first down and holding the football. You just don't want to get fancy right there."

The Eagles were forced to use their two remaining times out on the Redskins' next two plays, and though they eventually forced a punt, they had only 51 seconds to score from their 49.

A seven-yard pass from Jaworski to Montgomery ate up 27 seconds because Chris Hanburger collared the Eagle running back and prevented him from going out of bounds to stop the clock.

A pass to tight end Keith Krepfle got nine more, but again Redskin defenders kept him inbounds. Jaworski then stopped the clock with one second left by deliberately throwing out of bounds.

One second and 10 from the 35, Jaworski threw the ball deep and out of the end zone, but Redskin tackle Perry Brooks was called for jumping offsides. Given another chance, Jaworski dumped off a pass to Franklin at the 25, but the Eagle running back dropped the ball. End of game.

Philadelphia Coach Dick Vermeil insisted later that the play that buried his team was Green's punt return after the Eagles first possession of the second half.

"It definitely broke out backs," he said. "The coverage was too intense. Everyone was around Green, but they were looking for somebody else to make the tackle."

"When I fumbled the ball, I actually just thought about falling on it at first," Green said. "Eighty yards was the last thing I was thinking. But I saw a little hole and I tried to get an extra yard or two. I got lucky and got 80."

He got lucky because Redskin cornerback Gerard Williams got away with clipping punter Engles at midfield. Umpire Ralph Morcroft just happened to turn his back to avoid getting trampled and never saw the block.

"I don't know about that," said Pete Wysocki, who threw a key block on the play. "But when Tony burst through that little hole, all you could hear was the Eagles cursing. Tony did most of that on his own. He just shook it on down."

The Redskins also shook up the Eagles with that spectacular Theismann-to-Buggs touchdown pass 26 seconds into the fourth period.

The play started off as a handoff to Riggins, who veered toward the left tackle, then turned around and pitched back to Theismann.

"That's the first pass I've ever thrown in my life that I never had my fingers on the laces," Theismann said. "Its wasn't a picture pass, I can tell you that. But it did get the job done.

"Was it fun?% Are you kidding? John (Riggins) wanted to go back and change into his black hightops. You kind of feel like a fool, running with the ball and then pitching it back. But you don't feel like a fool when six points go up."

While Riggins was doing his spin-and-whirl number, Buggs was jetting down the left sideline. Eagle safety John Sciarra and cornerback Herman Edwards had come up to play the run and had no chance to recover. Buggs, who had four catches for the day, caught the ball alone at the two and stepped in for 35-16 lead that almost was not enough.

"I wish I could explain why we played so bad," said Redskin defensive tackle Diron Talbert. "You'd think we'd be able to hold that lead. They had so many points it's hard to tell why, whether it was field position, bad tackling or what.

"But give the offense all the credit in the world. They started slow and they finished slow, but they played well in between. Sure it's embarrassing to see somebody get that many points. But there's nothing embarrassing about winning. And that's all that counts."