The miracle men of Atlanta ran out of phenomenally fantastic finishes today, although they were able to throw a monumental scare into the defending National Football League champion Dallas Cowboys.

On a day when Cowboy quarter-back Roger Staubach was knocked out of action late in the first half, Dallas had to depend on reserve quarterback Danny White to rally it from seven points back at halftime to a 27-20 victory in theNFC semifinal playoff.

Scott Laidlaw's one-yard touchdown dive off left tackle, on a play that was supposed to be a pass, provided the winning points with 9:46 left in the football game.

that helped advance the Cowboys into the NFC championship game Jan. 7 against the winner of Sunday's Minnesota-Los Angeles game. A viking victory would allow the Cowboys to play that game here in Texas Stadium. A Ram triumph would mean a Cowboy gallop to Los Angeles.

The Cowboys had to pull out all the stops today against a Falcon team that had rallied so many times before this season. Atlanta won six times with two minutes or less showing on the clock, four in the final 10 seconds.

Dallas was not assured of this victory until safety Cliff Harris intercepted a Steve Bartkowski pass and returned it 22 yards to the Falcon 24 with 29 seconds to play.

But there were all manner of big plays for a Cowboy team that unveiled an offense with two tight ends to help block the blitzing Falcon defense, used a fake punt to set up one touchdown and made a born-again hero out of 38-year-old tight end Jackie Smith, who caught a second half touchdown pass-his first of the season.

After giving up 20 points in the first half, the Cowboys held Atlanta scoreless in the second half, yielding only 85 yards and five first downs.

That enabled the Cowboys to rally from 20-13 at intermission, even after Staubach, the team's most valuable player, was downed by a late hit by Falcon linebacker Robert Pennywell with 38 seconds left in the second quarter. Staubach's availability for the NFC title game will be determined later in the week.

"I was a bit tense when Roger was hurt," White said. "It was not like starting a game and knowing you are going to start. I was nervous, but I tried not to act like it."

Cowboy Coach Tom Laundry clearly had to be a jittery when he took his team into the dressing room at the half.

He said he told them they had "30 minutes left to play or we would go home. I think that got their attention."

But not right away. With Staubach, slightly dizzy and nauseous, watching on the sideline, the first pass White threw was intercepted by Falcon cornerback Ronald Lawrence.

White regained his composure soon enough. Back-to-back passes of 24 yards to Billy Joe DuPree and an across-the-field screen thrown to Laid- law that gained 15 gave Dallas first and goal at the two.

From there, looking for Smith.

"Jackie made a tremendous adjustment to get open," White said, and the quarterback dumped the ball off to his savvy tight end, who caught it a yard deep in the end zone. Rafael Septien's extra point tied the score at 20 with 7:07 left in the third period, and the Cowboys started taking control. The first of several decisive Dallas plays came early in the fourth quarter, when the defence forced a Falcon punt from Atlanta's 20-yard line.

Charlie Waters, the Cowboys' all pro safety and punt-blocker extraordinary, was lined up on the right side and came in on Falcon punter John James virtually untouched.

"I got real close and I had to make a decision to try and block it," Waters said. "I didn't think I could, so I just yelled at him I yelled, 'John' as loud as I could. I know him from the Pro Bowl, and I know I got his attention. I was just trying to distract him."

The tactic worked. James got off an ugly 10-yard kick and the Cowboys took over at the Falcon 30.

"Yeah, I heard him," James said "but's that's no excuse. I just feel like crying."

The cowboys felt like scoring.Despite an offside call that gave them a first and 15 at the 16. Laidlaw was not about to be denied his second touchdown, even if there was a mix-up in signals from the bench.

His 14-yard run off right tackle got the ball to the one, then confusion joined in the Cowboy huddle when wide receiver Drew Pearson brought in a play from the bench.

"The play that was sent in was called a slant 26." White said. "But we don't have a slant 26 in our goal-line offense. They had intended it to be 'fire slant 26,' which is a pass play. So I just called toss 36."

"It wasn't what Coach Landry had in mind," added Laidlaw, "but it did get the job done."

Laidlaw took a low dive off left tackle and landed three yards deep in the end zone. His second touchdown and Septien's extra point gave Dallas a 27-20 lead with 9:46 remaining.

No one in the crowd of 60,338 was breathing easily, however, though there was a healthy sigh of relief six minutes later.

The Falcons had mounted one of their typical fourth-quarter drives, moving from their nine to a first down at the Cowboy 41.Three plays later, it was fourth and one at the Cowboy 32 with 3:29 remaining.

Bartowksi pitched the ball back to Cleveland Franklin, who tried to pick up the yard off right tackle. But dallas linebacker Thomas Henderson slipped in to make the hit and corner-back Benny Barnes applied the finishing touches with a tackle for no gain.

"They had used the same play earlier in the game." Henderson said, "and Charlie Waters said in the huddle if they lined up in an I formation they'd use it again. They did, and we were ready for it.

"We had the angle on it from both sides. I made a move around the tight end-that's cause i'm so quick-and I almost got run over, but I stopped the man. I made the play. Benny assisted. Get it right."

The Cowboys got the ball with 3:09 remaining, gave it back to Atlanta at its 24 with 48 seconds remaining, then clinched the victory with Harris' interception.

Falcon Coach Leeman Bennett had nothing but praise for his team, and the Cowboys.

"Dallas, as everyone knows, is an excellent football team," he said, "and they proved it again today when they had a chance to go down the tube, losing their quarterback. Danny White threw the ball well and made the key completions when he had to."

White also showed a lot of class in the interview room, when he said, "I hope Roger isn't hurt seriously. He is the most valuable player to his team in this league. He's taught me so much on and off the field. I hope he can play.

"If I could be like Roger Staubach 10 years from now, "I'd consider myself a great success."

In Texas Stadium today, he was exactly that. CAPTION: Picture 1, Steeler John Stallworth makes difficult touchdown catch in fourth quarter, one of 10 completions for a playoff record. UPI; Picture 2, Roger Staubach of the Cowboys is unconscious (left) as teammates Tony Hill and Herb Scott (68) stand over him. UPI; Picture 3, The injured quarterback is helped from the field (right) after suffering concussion. His availability for next week will be determined later. AP