Washington decided the only way to beat Dallas in the season opener yesterday was to all but ignore the run and pass, pass, pass. But the Cowboys shot down that strategy by intercepting four of Joe Theismann's passes in defeating the new-look Redskins, 26-10.

By the end of the first game of Joe Gibbs' first game as head coach, some familiar sounds were filling RFK Stadium: boos. Many Redskin fans were roundly criticizing Theismann for his play and Gibbs for continuing to use the veteran quarterback.

"I still love our fans, they will treat us right," said Gibbs afterward. "There will always be some people who will boo when you are doing poorly."

Owner Jack Kent Cooke hired Gibbs to add pizazz to the Washington offense. So Gibbs began his NFL head coaching career by ordering 49 passes, one less than the team record, and 18 running plays.

Despite this imbalance, the Redskins kept putting together scoring threats, only to be thwarted repeatedly by Theismann's interceptions. One turnover came with Washington at the Cowboy 36, another at the 26 and a third at the four midway through the fourth period. That last mistake ended any hopes of a Redskin rally when defensive back Dennis Thurman returned the ball from his goal line to the Washington four, setting up the last of four field goals by Rafael Septien.

While the Redskins struggled, quarterback Danny White had the Cowboys performing in fine fashion. White threw touchdown passes of 33 and 42 yards and halfback Tony Dorsett shredded Washington's still-porous running defense for 132 yards. It was the first time he has gained more than 72 yards against the Redskins.

Theismann's only response to this was a 15-yard scoring pass in the second quarter to halfback Joe Washington, who was one of the Redskins' few standouts. The ex-Colt star caught 10 passes and ran for 17 yards on six carries. Otherwise, the Redskins had to settle for a lone 42-yard Mark Moseley field goal.

"Our basic idea coming in was that we didn't think we could run the ball on them, so we decided to go after them with the pass," Gibbs said. "As it worked out, we weren't very balanced."

The tactic shocked many of the Cowboys. Defensive tackle John Dutton said Washington "has to run the ball to be more successful. They have John Riggins, Terry Metcalf, Joe Washington and Clarence Harmon in the same backfield and I can't believe they didn't run the ball."

Entering the game, the Redskins weren't sure how well their young offensive line, with four new starters, would hold up against the Dallas front four, the best in the NFL.

That line allowed only three sacks and was praised by Gibbs. It was Theismann who came up with one of his poorest pro performances after enjoying a fine preseason.

Theismann wound up completing only 22 of 48 passes for 281 yards.

"But the fans shouldn't put all the blame on Joe," said tight end Don Warren. "I've never seen anyone who prepares harder for a game or knows more about a game plan. We just didn't have good execution. Our timing broke down. It's not his fault."

However, Theismann, who has been overjoyed because he finally is playing for an offensive-minded coach, said he made "some very poor decisions. I felt like the offensive line played super and the defense was super but I made poor decisions. In all our exhibitions, the key to success was not making mistakes. I didn't feel bothered by the rush."

Theismann was bothered by a patched-up Dallas secondary. The more Gibbs studied that secondary, the more he was convinced the Redskins could exploit it. And that was before starting cornerback Steve Wilson left the game with cramps, rookie free safety Mike Downs pulled a hamstring and linebacker Mike Hegman broke his forearm.

Even with rookie free agent Everson Walls at cornerback and reserve Bennie Barnes at free safety, Dallas kept forcing turnovers, including two fumbles, one by Theismann on the last play of the game.

The Redskins also were bothered by a Cowboy offensive blocking scheme that tackle Dave Butz called "the best I've ever seen. They kept giving us confusing blocking reads up front that kept us off balance. It allowed Dorsett to run so well."

When the Cowboys opened by running well inside and outside on early downs, the Washington defense, 25th against the run last season, likewise was thrown off balance.

"We adjusted but we never could get settled," said strong safety Tony Peters. "I knew they would run, but not that well. We couldn't stop it. We wanted to force them to pass but we never could come up with a way to cut down on those early-down runs. That beat us, no question."

Dallas averaged almost five yards a rush (Dorsett gained six yards an attempt) and wound up with 206 yards on the ground to Washington's 44. White threw 24 passes, completing 12 for 145 yards. He was sacked only once in the face of an inconsistent pass rush. And the better the Cowboys ran, the more tired the understaffed Redskin defense became.

Theismann found out early that the Dallas secondary was tough. On the opening possession of the game, he had the Redskins on the Dallas 36 before he tried to find Ricky Thompson deep over the middle. His forced throw was picked off by Downs, who pulled his hamstring on the return.

Dallas soon had the ball at the Redskin 12, but a fumble by Dorsett, a fine tackle by linebacker Monte Coleman on a screen pass and Coy Bacon's sack preceded a punt on fourth and 33.

A fumble by fullback Ron Springs at the Washington 25 ended another threat moments later, but the Cowboys finally scored on their third possession, when tight end Billy Joe DuPree made a one-handed diving grab of a 33-yard pass by White in the end zone.

Washington took the ensuing kickoff, and with the help of a 22-yard reception by Riggins, moved to the Cowboy 20, where Moseley came in and kicked an apparent field goal. But Dallas was called for too many men on the field and the Redskins got a first down at the 15. Theismann immediately hit Joe Washington with a swing pass, and he sprinted by two tacklers into the end zone to tie it up.

Receiver Drew Pearson beat cornerback Jeris White midway through the second period, catching a 42-yard scoring pass before free safety Mark Murphy could get over to help out, giving Dallas a 14-7 halftime lead.

While Septien was adding four second-half field goals, Theismann was getting more frustrated. With Dallas ahead, 20-10, in the fourth, on a second-and-three situation, he rolled to his right from the Dallas 25 on a planned play and threw what he called a dumb pass. The pass went up for grabs and into the hands of Walls, a free agent from Grambling State.

Then, with the Cowboys leading, 23-10, Joe Washington moved to his right, pulled up and passed a high floater to Warren, who was all alone along the left sideline. Warren got to the nine before being dragged down. But three plays later, Theismann tried to hit Art Monk down the middle of the Cowboy defense. Thurman tipped the ball with one hand, pulled it in and took off, only to be caught from behind 96 yards later by Joe Washington at the four.

Thurman said he had Monk "man to man. We were in a blitz. Theismann just pumped it in there, I had one step. They say I'm not fast enough to score but I went 96 yards with it."

Gibbs said he told his players "they kept coming up with the big plays and we couldn't. It comes down to that. They're a darn good team and we needed better execution. Today, we didn't get it."