Rookie quarterback Phil Simms showed the poise of a veteran today but the New York Giant veteran defenders lost theirs and the Dallas Cowboys came from behind for a 16-14 victory.

Rafael Septien's third field goal, a 22-yarder with three second to play, provided the margin of victory for the Cowboys, NFC East leaders, who trailed by eight points with 8:33 to play.

The Cowboys were struggling at that point, before Roger Staubach, Tony Dorsett and Septien took matters in hand as the Cowboys (8-2) expanded their division lead to two games over Washington and Philadelphia, both losers today.

Staubach spirited the Cowboys 72 yards to narrow New York's advantage to 14-13 on a 32-yard touchdown pass to Drew Pearson and Septien's conversion.

Staubach then gave a clinic on how to execute the two-minute drill, whipping his troops 86 yards to the New York five, mostly on a 32-yard screen pass to Dorsett.

Septien's field goal followed, leaving Giant rookie Coach Ray Perkins virtually speechless.

Perkins was envisioning a big upset for the second straight week, after Simms threw two touchdown passes, 32 yards in the second quarter and 23 in the final period.

The Giant coach was so distressed by his team's defensive breakdown that he said in the dressing room, "I'll ask you to forgive me; this is going to be short. We played a very fine football team, and we were a very fine football team today."

He left the interview session without accepting any questions.

The Giants were soaring in confidence after upsetting the Los Angeles Rams a week ago and the largest crowd ever to see them play here -- 76,400 -- harked back with cheers to the days of Sam Huff and defensive superiority when the Cowboys were stopped at the New York one-foot mark on fourth down in the first half.

The Giant defense almost came up with the big play on the final Cowboy drive. Linebacker Brad Van Pelt tackled Dorsett to end the 32-yard pass play. Dorsett bobbled the ball but held on.

"I was scared to death," Dorsett said. "The linebacker popped me, the ball popped up out of my hands, but it dropped back in my hands."

From the Giant 12. Dorsett was thrown for a yard loss, Staubach was then sacked for a loss of four yards by linebacker Brian Kelley, back to the 17.

But Dorsett broked off a 12-yard run around his right end and got out of bounds at the New York five to stop the clock.

Septien hummed the ball through the upright from 22 yards out and Dorsett put the happening in perspective: "Football is a 60-minute game, and with our potential and my Godgiven talents, anything can happen. We rose to the occasion like champions.

'The Giants were expecting us to throw a deep pass before the screen pass to me, because I dropped back as though I was going to block."

Simms tried to blame himself for a large part of the loss. He had a pass intercepted in the first period which the Cowboys converted into a 3-0 lead onb Septiens's first field goal, a 26-yarder.

"To be honest," Simms said of his intercepted pass, "I just didn't read the defense; you just can't do that."

In a thoughtful reference to the Giant offensive line, he said, "I didn't get hit once; that's nice." Actually, he was sacked once.

Simms conpleted 10 of 16 passes for 150 yards and picked out his targets in a deliberate style. The No. 1 draft choice from Morehead State engineered a 75-yard assault on the Dallas defense in the second quarter, as if he had not been bothered by the interception at all.

Simms zipped the ball over a linebacker and daringly into the coverage of two other defenders for the 32-yard touchdown pass to wide receiver Johnny Perkins.

In the fourth period, Simms propelled the Giants 36 yards to score after Cowboy wide receiver Tony Hill fumbled on an end-around play. Simms dropped straight back, waited for running back Billy Taylor to complete a circle pattern in the end zone, and lofted the ball over the linebackers and about 15 yards away from free safety Cliff Harris, who earlier had punished the quarterback with a blitz.

"He is as good a quarterback as I have seen in his first year," said Cowboy Coach Tom Landry, "He is in the mold of Bert Jones (of Baltimore). It is a rare quarterback who steps in and wins as a rookie."

Simms had led the Giants to four straight victories as a starter, after they had a 0-5 record.

"The Giants' potential is better than I have ever seen, with Simms and that wide receiver (Ernest Gray)," Landry added.

Staubach hit on 20 of 30 passes for 266 yards but for the second straight week was treated roughly. He was sacked four times after suffering a concussion a week ago in Pittsburgh. Dorsett caught six of those throws, for 68 yards, to go along with his mere 36 yards rushing in 16 carries.