By losing, 24-10, to the Dallas Cowboys today, the Redskins once again proved they can't compete against more talented opponents unless Joe Washington stays healthy and their nickel defense improves dramatically.

Washington, the gifted veteran halfback, left the game just before halftime with a rib injury. Before he departed, the Redskins appeared capable of upsetting Dallas. But those hopes, and a four-game Redskin winning streak, were erased when Washington did not play the second half and Cowboy quarterback Danny White kept completing passes almost every time he was faced with a long-yardage situation.

To compound the Redskins' difficulties, their defensive backs were incapable of holding onto what should have been at least five interceptions. That allowed the high-powered Dallas offense to control the ball and gradually overwhelm the slower Washington defense.

Although the defeat didn't eliminate the Redskins (5-7) from gaining a wild-card spot in the NFC playoffs, it probably means they have to win their last four games, against Buffalo, Philadelphia, Baltimore and Los Angeles, to stay in contention. The way they played today, that is going to be difficult.

Not that the Redskins were routed by Dallas (9-3), now tied with Philadelphia for the NFC East lead. Washington had the game tied, 10-10, with 11 minutes left in the third quarter, even after botching two scoring opportunities in the first half by throwing an interception and missing on a short field goal kick.

But when they had to, the Redskins were incapable of producing an important play, either on offense or defense. And the Cowboys, a much quicker, deeper team, kept coming up with big plays.

The biggest occurred shortly after the Redskins had tied the score on Mark Moseley's 26-yard field goal with 11:05 left in the third period.

Just after cornerback Jeris White dropped an interception with the field in front of him wide open, Danny White faced a third and 18 at his 46. He was forced out of the pocket and was almost out of bounds, running to his right with tackle Dave Butz in pursuit, when he unleashed a pass down the middle of the field.

Receiver Drew Pearson had broken free beyond the Washington linebackers and caught the throw for a 34-yard gain despite a savage hit by safety Mark Murphy. Five plays later, White connected with tight end Doug Cosbie for a 10-yard touchdown on another third down and Dallas was ahead for good, 17-10, with 5:52 left in the third period.

"I really thought Pearson dropped the ball," Murphy said. "I saw the ball bounce and then go back into his chest. But it still was a great play. We never were in control. We were scrambling the whole game. We had to fight to stay in all the way."

From the Redskins' standpoint, their most important play came with 39 seconds remaining in the first half, when Joe Washington ran nine yards to the Dallas seven. While turning to gain all the yards he could on the draw, Washington felt the cartilage in his left rib cage rip.

"I wasn't hit or anything," he said. "It hurt. I couldn't breathe, I couldn't hardly swallow. I couldn't bend over. I gave thought to going back in (in the second half) but it would probably have hurt the team more than help it."

The Redskins did score on the next down when Joe Theismann completed a seven-yard pass to halfback Nick Giaquinto, a waiver pickup from Miami two weeks ago, to trail, 10-7. But their offense was woeful without Washington in the second half.

Before he was hurt, Washington had gained 84 yards on 12 carries and caught three passes for 47. Those 131 yards were 67 more than the Redskins would gain the entire second half, when they were limited to 64, 30 on the ground. When the Cowboys realized the Redskins no longer could run successfully, their front four began teeing off on Theismann.

"It's not an excuse, but we just aren't the same team without Joe Washington," Coach Joe Gibbs said. "He gives us a dimension that we need. Losing him and not being able to make the big plays were the difference. We dropped interceptions, we missed chances for at least nine points and we let them complete a lot of long passes. As long as we could stay in normal down and distance situations, we played them pretty good."

Dallas gained 470 yards, 258 rushing. Tony Dorsett, despite a sore ankle, gained 115 yards and fullback Ron Springs a career-high 85 as the Cowboys had great success running around the Redskins' right side. Washington kept juggling players, benching end Dexter Manley for most of the game and linebacker Monte Coleman for parts of it, but Dallas was just too strong and too fast.

Yet those third-down passes hurt the Redskins most. The Cowboys got first downs on 64 percent of their third downs, including eight when they needed at least nine yards for a first down.

"They executed very well," safety Tony Peters said. "They're a good team. But it hurt not to score early when we had a chance. You have to get points against them whenever you have a chance."

Washington's value to the Redskins was never more obvious than during the drive on which he was hurt. Trailing, 10-0, with 92 seconds left in what had been a discouraging half, the Redskins moved 51 yards in four plays to score.

Washington picked up all but seven of those yards, twice catching short passes and turning them into 20- and 15-yard gains with his ability to twist and turn past would-be tacklers in the open field. Then he got nine yards on the draw play that ended his contributions for the day.

Earlier in the half, the Redskins had moved to the Dallas nine, only to have Moseley miss on a 27-yard field goal kick. Then, after White threw a 28-yard touchdown pass to Butch Johnson on a third-and-12 play for a 7-0 lead, Washington marched to the Cowboy 22, only to have safety Charlie Waters intercept Theismann's pass into the end zone.

"I didn't see Charlie," said Theismann, who was 14 of 34 for 158 yards. "He got lost in the shadows down at that end of the field. I saw Terry Metcalf and he was open ahead of his man. I let the ball go and then Charlie came visible and I said, 'Oh, oh.' "

The Redskins' tying field goal was set up by Mike Nelms' 51-yard kickoff return to the Cowboy 42. A 16-yard pass to Ricky Thompson got a first down at the 15, but defensive end Ed Jones knocked away a third-down pass to bring on Moseley for his 26-yarder.

Once Dallas went ahead, 17-10, the Redskins had just one more scoring opportunity. Giaquinto, who played decently as Washington's replacement, caught two passes and ran a draw for 13 yards and the Redskins were at the Dallas 25. But an incomplete pass forced Moseley to try a field goal from 48 yards and the kick went off to the left.

And, faced with a savage pass rush, Washington couldn't produce another first down the rest of the game. Dallas didn't score its final touchdown until fullback Ron Springs went over from the one with 52 seconds left. Twice, Theismann almost was sacked for a safety, first by Randy White, then by Harvey Martin.