When Tony Dorsett runs for nearly 100 yards, as he did here today, the Cowboys usually win. But because linebacker Andy Headen dashed 81 yards for a touchdown with one of three Dallas fumbles, the Giants scored a 28-7 upset.

As almost always happens, the Giants were the less heralded team; as sometimes happens, they clearly were better. Linebacker Lawrence Taylor caused that momentum-turning fumble and one other, and Phil Simms passed for three touchdowns.

"Ten years of frustration," said veteran defensive lineman George Martin, "and now to beat a team like Dallas like we beat them. And to be in first place, too. It's too much for me to handle."

The Giants began handling the Cowboys early. On their third possession, Simms passed over the middle to new hero Byron Williams. He squirted from Everson Walls' grasp and outran two other Cowboys to complete a 62-yard pitch-and-catch.

"When I broke Walls," said Williams, "I knew I was gone."

"We have so many kids on this team," Martin said, "and their attitude seems to be that they don't know they're supposed to lose."

The Giants' defense was nasty from the start, with such as safety Terry Kinard breaking up pass plays with wicked hits; he set up the Giants' second touchdown with an interception and 29-yard return to the Dallas 16.

Immediately, rookie Lionel Manuel drifted behind the Cowboys' secondary and made his first NFL reception a touchdown. The play is one the Giants had worked on most of the week to spring on the Cowboys.

It went to Manuel, Coach Bill Parcells explained, "because he comes out of the cuts faster than anyone we have."

Taylor comes out of the blocks faster than anyone else his size, and when the Cowboys failed to cover him on a blitz he stripped Gary Hogeboom of the ball and started Headen running for a 21-0 lead.

The same situation came shortly before halftime, Taylor again crashing on a blitz and causing a Hogeboom fumble Kinard fell on at the Giants' five.

Ron Fellows fumbled the second-half kickoff, the Giants recovered and, 16 seconds into the third quarter, Simms hit tight end Zeke Mowatt in the end zone from 18 yards.

The celebrating in Giants Stadium took on new intensity, as did admiration for the Giants suddenly being able to produce touchdowns instead of field goals from inside an opponent's 20-yard line.

"The defense is making big plays, like they always do," Simms said, "and now we're making them count."

"Last year," said defensive lineman Jim Burt, "we'd make a big play and they'd fumble. This year, bingo, they score. We're doing like the Redskins have done, turning turnovers into touchdowns.

"That's been the only difference between the Redskins and the rest of the (NFC East). We've got a San Diego kind of offense."

They also have a second-year coach still coming to terms with the negative parts of his profession. Dragging on a cigarette, he was almost alone on the way to an elevator an hour after game's end.

"Might sleep tonight," he said. "Don't know."

Later, in the elevator, Parcells admitted how distressingly brief his happy times had been.

"Know the first thing I thought about when I walked off the field?" he said. "The Redskins next week."