The Dallas Cowboys never knew what hit them until it was too late tonight and tumbled from the ranks of the unbeaten without much of a fight.

The Cleveland Browns staggered them with a 20-point first quarter and contained the defending National Football Conference champions so handily that the crowd of 80,123 became bored and began souting, "We want Pittsburgh," with more than 8 minutes remaining.

The 26-7 loss put a new face on the NFC East Division standings as the Cowboys dropped into a tie with the Washington Redskins and Philadelphia Eagles at 3-1.

The Browns are up there with the Steelers at 4-0 in the AFC Central Division because Brian Sipe's sharpshooting embarrassed the Cowboys' pass defense from the outset.

The Browns wrought the victory with Greg Pruitt sitting out the second half with a strained knee. Sipe threw two touchdowns in the opening quarter, 23 yards to Dave Logan and 52 to Ozzie Newsome.

Free safety Thom Darden ran back the first of two interceptions of Roger Staubach passes 39 yards for a touchdown and Staunbach never did get his troops organized for a serious comeback. He did avert a shutout with a 48-yard pass to Tony Hill in the first period after Cleveland sped into the 20-0 lead.

But Sipe engineered another touchdown in the fourth quarter, a two-year plunge by Mike Pruitt, and it was accomplished with 13 minutes 55 seconds still to play.

Former President Gerald R. Ford was a guest of Art Modell on the happy occasion for the Browns' owner and saw defensive end Mike Sinclair of the Browns exude so much confidence about the outcome with 11 minutes to play that he reawakened the fans by leading cheers during a timeout.

Cleveland manhandled Staubach overrun his offensive line. He completed 21 of 39 passes for 303 yards, but they were mostly of the catch-up variety and he suffered four sacks, Darden's interception was the first against Staubach in 151 this season.

Sipe completed 15 of 28 for 239 yards, was intercepted once and sackled once. He tried only 12 throws in the second half.

Meanwhile, Staubach lost two fumbles and Scott Laidlaw one, the Cowboys dropped passes and Rafael Septien missed a 47-yard field goal and had a 34-yarder blocked.

At least one Cowboy didn't take the licking passively Thomas Henderson played a thoroughly energetic and at time overpowering game. He accounted for one of the two conversion attempts Don Cockcroft had blocked, shook up Sipe twice with driving tackles and was all over the field.

For the rest of the Cowboys, it was one of the worst-played second quarters ever.

Tony Dorsett managed 64 yards in 14 carries, but had little help. Wide receiver Drew Pearson ended up with five receptions for 109 yards as nine different Cowboys shared Staubach's deliveries.

"The Cowboys turned the ball over in critical situations, and it's a credit to us that we came up with the big play," said Sipe.

"This is the most dramatic game I've ever been involved in," said Cleveland Coach Sam Rutigliano. "The key? We played opportunistic football."

Said Staubach: "Tonight we made mistakes. But the Browns caused them."

"They're rolling now," said Henderson.

"They're not. They're screaming out there like they're the University of Oklahoma. I don't think much of their offense though. Did they get some breaks? They must have had a fairy godmother out there."

The Browns took it right to the Cowboys after accepting the opening kickoff. Sipe picked on rookie cornerback Aaron Mitchell on a pass to running back Greg Pruitt for 27 yards, and wide receiver Dave Logan beat cornerback Aaron Kyle for a 23-yard touchdown in a 63-yard flight to the Dallas goal line, 60 yards coming by air.

Sipe then whipped the Browns 61 yards on another air sortie, making free safety Cliff Harris look leaden as tight end Ozzie Newsome ran away from him for a 48-yard touchdown catch.

On third and four at the Dallas 35, Darden pretended to be caught out of position, but when Staubach unloaded Darden swooped in on the ball, tucked it to his chest and ran 39 yards for a score.

That all happened with only 6 minutes and 5 seconds gone in the game.

The Cowboys interrupted Cleveland's momentum momentarily when Tony Hill raced under a bomb by Staubach, caught the ball in stride at the Browns' 12 and went the rest of the way for a 48-yard touchdown with cornedback Ron Holton burned on the play.

From there on, the Cowboys went through the motions as if content to get a bad game out of their system before taking on Cincinnati at Dallas Sunday.

The Browns' fans will have to wait two weeks before seeing their heroes take on Pittsburgh, but face a high risk Sunday at Houston.