In a game that will be dissected and cursed for days to come in Washington, the Dallas Cowboys rallied from a 23-3 halftime deficit last night to defeat the Redskins, 31-30, in a nationally televised season opener before a sellout of 55,045 at RFK Stadium.

The Redskins were so competent in every way in the first half, but the walls of their Jericho came crashing down in the second half.

After quarterback Danny White, held to one measly completion in the first half, threw touchdown passes of 75 and 51 yards to wide receiver Tony Hill, closing Dallas within 23-17 with 6:35 left in the third quarter, the Redskins' trouble multiplied again and again.

That's when, fittingly enough, Dallas became Dallas.

The Redskins missed a chance to take a 26-17 lead when Mark Moseley, good on three first-half field goal attempts, missed wide right on a 31-yarder with 9:24 left.

"It wasn't even close," Moseley admitted. Consequently, the Cowboys were still within six points.

Deliberately enough, they then marched to victory. White finished the game-winning drive by outrunning linebacker Rich Milot around the right side for a one-yard touchdown with 2:20 left, finishing a 12-play, 80-yard drive. Rafael Septien's extra point gave Dallas a 24-23 lead.

Washington quarterback Joe Theismann, who completed 28 of 38 for 325 yards and two touchdowns, tried to generate a comeback.

There were no heroics in the humidity, though: on second and 10 from the Washington 20, Theismann threw a pass intended for wide receiver Charlie Brown, who said later he ran the wrong pattern. The pass was intercepted by cornerback Ron Fellows, who caught the ball near the sideline at the Washington 37 and returned it to the four with 2:03 left.

Three plays later, White threw a one-yard touchdown pass to tight end Doug Cosbie, giving Dallas an insurmountable 31-23 lead with 1:54 left and giving the Redskins cause to scratch their heads and wonder, "What happened?"

The Redskins managed to score a touchdown on a one-yard pass from Theismann to tight end Don Warren with 10 seconds left, closing within one point as so many fans were quietly leaving a stadium they had percolating in the first half. There were no Fun Bunch celebrations for this touchdown.

"It was two completely different games," said Dallas Coach Tom Landry. "In the first half, I don't think I've seen a team play better than Washington. In the second half all we had to prove was that we could come back."

Strange, how a team could lose a game when it had a time of possession advantage of 37:18 to 22:42. Last night, though, it happened.

Washington Coach Joe Gibbs said, "At halftime we talked about keeping up the tempo, staying aggressive and not going into a shell. We were especially concerned about not giving up a big play in the first five minutes. It was a tough loss, a very tough loss."

The Dallas reversal spoiled a first-half Washington masterpiece, a masterpiece made possible by, among others, Alvin Garrett, Smurf wide receiver who caught 10 passes for 101 yards in the game, taking advantage of the room afforded him by cornerback Everson Walls.

In the first half, the Redskins' special teams kept Dallas pinned in poor field position. The Cowboys' best field position in their six first-half drives came when they started from their 21.

"We weren't flat," Landry said. "We just never got the ball where we wanted it."

The Redskins opened the game with an impressive 13-play, 66-yard drive. Running back John Riggins, who gained 89 yards in 27 carries, ran five times for 14 yards. Theismann hit Garrett for key gains. But the Redskins stalled and settled for Moseley's 23-yard field goal with 8:35 left in the first quarter.

As defensive end Dexter Manley led a pass rush that swarmed White and held the Cowboys to five net yards in their first two possessions, Washington dictated the tempo. Theismann and Garrett kept working over Walls. Riggins ran one yard for a touchdown, giving the Redskins a 10-0 lead with 48 seconds left in the quarter.

Almost instantly, Dallas revived. It happened when Tony Dorsett, who gained 151 yards in 14 carries, followed a block by running back Ron Springs at the line of scrimmage at the Dallas 17, and swept down the left side for a 77-yard gain, to the Washington six.

Dorsett was stopped from scoring a touchdown by rookie cornerback Darrell Green, who raced past two teammates to catch Dorsett. Really, Green saved the Redskins four points because the Cowboys were relegated to Septien's 26-yard field goal. That made it 10-3 with 14:46 left in the half.

Subsequent Redskin drives were finished with field goals from 30 yards and 39 yards, the latter coming with 3:25 left in the half. The Redskins led, 16-3.

When White, who completed nine of 20 for 193 yards (one of nine for 10 yards in the first half), had his next drive cramped, Theismann led the Redskins 57 yards in five plays over the final two minutes.

On second and 16 from the Dallas 41 with 40 seconds left, Theismann threw to Brown, who caught the ball near the Dallas 15 between defenders Michael Downs and Dennis Thurman, then trotted into the end zone for a 41-yard touchdown.

The Redskins were saluted with a standing ovation as they went to the locker room with their 23-3 halftime lead.

"We just decided to come out and put it together for pride," said Dallas wide receiver Butch Johnson. "If we lost, well okay. But we put it together."

Oh, how the Cowboys put it together in the second half. On consecutive third-quarter possessions, Hill sped past the suddenly vulnerable secondary and scored touchdowns.

First, White dropped back on second and six from the Dallas 25 and threw to Hill. He sped down the left sideline, then curled over the middle past cornerback Vernon Dean, caught the ball beyond midfield and romped into the end zone.

This 75-yard touchdown pass brought Dallas within 23-10 with 12:20 left in the third quarter. White wasn't finished, either. He again located Hill, this time running down the right sideline, for a 51-yard touchdown pass.

On the next drive, Hill caught White's pass just beyond the tight coverage of cornerback Anthony Washington, who leaped in futility then fell near the Washington 20. Hill galloped into the end zone with the touchdown that closed Dallas within 23-17 with 6:35 left in the quarter.

Dallas made a strategy change in the second half, moving its cornerbacks to the line of scrimmage, then dropping them back to take away Theismann's chance to call audibles. Theismann still completed 14 of 19 passes in the second half, but the offense did not produce.

The Redskins seemed ready to reverse the Dallas onslaught. When Theismann completed a nine-yard pass to Warren, Washington had an apparent first down at the Dallas five with about 10 minutes left. But Warren was penalized for offensive pass interference, moving the ball back to the Dallas 24.

Then Moseley lined up for a field goal that could have put the Redskins ahead, 26-17. He missed.

RFK Stadium fell silent. Then the Cowboys, advancing when they had to, followed Dorsett and Springs and were aided by a crucial 15-yard spearing penalty against linebacker Mel Kaufman that moved the ball to the Washington 35.

On second and goal from the Washington one, White ran for the touchdown that tied the score.

The Redskins' spirit was broken. Dallas had become Dallas once again.

Monte Coleman, who was scheduled to start at left linebacker, was taken to Sibley Hospital yesterday morning after he began hemorrhaging in his left thigh.

Coleman bruised the thigh in the Redskins' final preseason game at Buffalo. He practiced Thursday and Friday, but aggravated the injury and was held out of Saturday's practice; he was still complaining of pain Sunday. The hemorrhaging was discovered yesterday morning and Coleman was admitted to the hospital, where he was scheduled to remain at least overnight.

Trainer Bubba Tyer said, "The thigh looks today what it should have looked like the day after the game." He said it was swollen about two inches; Coleman is doubtful for Sunday's game at Philadelphia.

Mel Kaufman, who started in Coleman's place last season after Coleman was out with a shoulder injury, started last night.

Receiver Mark McGraff suffered a sprained shoulder and is also doubtful for the Eagles, according to Tyer. Guard Russ Grimm also sprained a shoulder but is expected to play Sunday. Mark May has a bruised shoulder and also should be all right.

Wide receiver Alvin Garrett of the Washington Redskins was identified incorrectly in a photo yesterday.