Trailing the New York Giants by 13-10 in the fourth quarter today, the Philadelphia Eagles sent Wilbert Montgomery up the middle on second and 42 from their own 14. He gained two yards, while boos reverberated around Veterans Stadium.

It was a better call than the one that followed, however. On third and 40, quarterback Ron Jaworski sent a cross-field toss in the direction of wide receiver Charles Smith. Cornerback Terry Jackson cut in front to intercept, galloped 32 yards to the end zone and the Giants were 20-10 winners, ending a 12-game losing streak to the Eagles that dated back to 1975.

Until he became the hero, Jackson had been charged with both defensive holding and pass interference, besides dropping what seemed an easy interception. But that one play erased all previous errors for both Jackson and the Giants, who achieved the remarkable upset by capitalizing on the futility of a team whose performance belied the 9-2 record it carried into the contest.

Large segments of the crowd of 66,827 started the boo routine early in the second period, picking first on a usually stalwart defense that today was guilty of leaving Giant receivers unguarded often enough for New York to march 73 yards to a touchdown and a 10-7 lead.

The bulk of the displeasure was reserved for Jaworski, who completed only 20 of 45 for 187 yards, was sacked three times and was frequently serenaded with "We want Joe," in honor of second stringer Joe Pisarcik.

Punter Max Runager, not needed in last week's 38-13 victory over Baltimore, showed signs of rust today. It was his nine-yard shank, out of bounds at the Eagles' 32 early in the fourth quarter, that set up the tie-breaker in what had stood as a 10-10 bore since halftime.

Even more startling was the postgame revelation that the play was supposed to be a fake punt, with the snap going to short man Frank LeMaster on the fourth-and-one situation at the Eagles' 23. But the normal long snapper, Mark Slater, had served as the tight end on the previous play, so center Guy Morriss filled in and goofed, with the surprised Runiger booting it off target.

Five carries for 19 yards by Rob Carpenter preceded Joe Danelo's 30-yard field goal, his second of the game, and with 9:35 remaining the Giants had a 13-10 edge.

Starting at their 24, the Eagles advanced as far as the 44 on a pass interference call against Jackson, then were pushed back to the 14 by an illegal use of hands penalty, an illegal block and a sack. Then came Jackson's game-clinching touchdown.

"They sent two men into my zone and tried to make me take Harold Carmichael," Jackson said. "But he was looking at Charles Smith all the way. Looking toward the sidelines made Carmichael's move meaningless.

"When he let the ball go, I knew I had it and I knew I'd score, because everybody else was back there blocking. The ball took a long time coming, because he was throwing 40 yards for an 18-yard gain. If I don't get to that, I shouldn't be on the field."

"That was probably a stupid call on my part," said Eagle Coach Dick Vermeil. "I knew they would be in that damn prevent defense and they just laid back there and picked off a fly pattern.

"They outplayed us, they outhit us and they outcoached us," said Vermeil, who was losing to New York for the first time in 12 meetings since he took over here in 1976.

Montgomery picked up 102 yards in 25 carries, the first runner to top 100 against the Giants this year. But he paid a price, twice needing treatment after being blasted on pass receptions.

Jaworski was hurt most of all, by those boos: "Fans have their opinion, and they're entitled to it, and my only feeling is that there are times when we need the fans behind us instead of against us. I think they were a little bit against us today."