After two straight second-half thrillers, the Washington Redskins finally produced a laugher last night by overwhelming the lethargic New York Giants, 27-0, to extend their unbeaten RFK Stadium streak on Monday night television to eight games.

It was hardly a memorable contest, but the Redskins were able to blend an opportunistic defense with the passing of Joe Theismann and three crucial New York penalties to bring their season record to 2-1.

The defense intercepted two Joe Pisarcik passes, one for a touchdown, registered three sacks and did not allow the hapless Giants to get anywhere near the Washington goal line. The best New York could do was to try an unsuccessful 48-yard field goal.

The game was not dominated by Washington as much as the score indicates, however, especially during the first half when New York's defense stopped the Redskin rushing game.

But Theismann's accurate passing -- he was 18 of 28 for 153 yards and one touchdown -- and the inability of Pisarcik to throw consistently thwarted any chance New York had of picking up its first victory of the season.

Besides tossing four yards to Clarence Harmon for one touchdown, Theismann ran seven yards for another. Defensive end Karl Lorch registered the first six-pointer of his professional career on a 31-yard run with an interception and Mark Moseley kicked field goals of 46 and 40 yards.

Moseley's successful kicks allowed him to break Curt Knight's team field goal record of 101. Moseley now has 102.

This was Washington's first shutout since December 1977 and its largest margin of victory since smashing the Giants, 49-13, in 1975.

Pisarcik, who had been sacked 14 times entering the game, was awful. His passes lacked zip and anytime he felt pressure from the veteran Redskin front four (Dave Butz sat out with a bad knee), he unloaded the football.

He was only seven of 24 for 112 yards on the night. Ironically, his poor showing came on an evening when the Giants, who had been averaging 51 yards rushing this season, mounted a decent ground game. Their 113 yards were more than they had gained in the first two contests.

But despite occasional bursts by New York runners, including a season's best for the team of 17 yards by Doug Kotar, Washington was able to shut off any threats once New York crossed the 50.

The Redskin offense did not get unwound until early in the third period. Until then, two New York penalties and Lorch's interception had been the difference in the game.

Moseley put the Redskins ahead for good with his 46-yarder in the first period. The kick was set up by a 22-yard pass from Theismann to reserve halfback Buddy Hardeman, who had five receptions.

To overcome the Redskin pass rush, Pisarcik was retreating and passing quickly. Those tactics backfired midway through the second quarter when Lorch, closing from his left end position, stepped in front of Pisarcik's lob into the flat and picked the ball out of the air. Lorch rumbled untouched to the end zone for a 10-0 Redskin advantage.

In the eyes of the Giants, that's how the half should have ended. But on the final Redskin possession, New York was called for two hotly contested penalties that enabled Washington to have a 17-0 lead at intermission.

The first yellow flag came on Mike Bragg's punt from the Washington 56. Linebacker Brian Kelley was cited for running into Bragg and the Redskins had a first down. New York Coach Ray Perkins disagreed with the decision so much that he slammed his clipboard to the ground.

Theismann passes of eight yards to Jean Fugett, who played despite a bad knee, and 18 to Ricky Thompson moved the ball to the 18 and 25 seconds left in the half. A toss into the flat to Hardeman left Washington a yard short of a first down. Coach Jack Pardee decided to try a field goal on fourth down instead of going for a first down from the nine.

Moseley failed on the 25-yarder, but Ray Rhodes was called for touching Moseley's leg on the kick. That gave Washington a first down at the four and Theismann, on the next play, passed to a wide-open Harmon in the end zone.

Perkins was incensed. Assistant coach Bill Belichick charged after referee Ben Dreith when time ran out and gestured wildly before going to the locker room.

Washington put the game out of reach by scoring on a 79-yard, 16-play march on its first possession of the third period.

Again, the Redskins benefited from a Giant penalty. Washington was facing a punting situation from its 17 but Kelley was caught roughing Benny Malone on a running play and the Giants lost another 15 yards.

Theismann took it from there. He scrambled for eight yards, passed to Danny Buggs for nine and found Fugett for 13. And the Redskin running game finally helped out after being throttled in the first half by the aggressive Giant defense.

John Riggins, who had 52 yards on 15 carries, ripped off gains of eight and nine yards to get the ball to the Giant nine. On third down from the seven, Theismann dropped back and, on a planned play, ran a quarterback draw up the middle, spinning the last yard into the end zone for a 24-0 Washington lead.

Now the Redskins could tee off on Pisarcik, who resembled a gun-shy fighter. On the ensuing series, he threw two wild passes into the Redskin end zone from the Washington 39 before a third heave was intercepted by Lemar Parrish behind the goal line. It was Parrish's third interception of the season.

This time, the Redskins mounted a 13-play thrust that burned up almost eight minutes. Theismann moved his team behind passes of 12 and nine yards to Thompson, six to Hardeman and 10 to Buggs, putting the ball on the Giant 23.

But the Giants' first sack of Theismann and an offensive interference penalty temporarily cooled off the threat. On third down, Hardeman gobbled up 22 yards on a draw and Moseley came in to boot his record-breaking field goal.

Veteran Paul Smith, subbing for Butz, was credited with nine tackles and three assists. Coy Bacon, the team's best pass rusher, had 2 1/2 sacks while Diron Talbert shared in one.

The Redskins got added pleasure from the victory by stopping former teammate Tony Green. Green, cut in preseason after making the Pro Bowl last year as a rookie, returned Bragg's three punts 12 yards and averaged only 17 yards on five kickoff returns.

He also was the victim of the best hit of the night, a smashing tackle by rookie Neal Olkewicz from Maryland.

The Giants finished with 206 yards, Washington 282. After being held to 35 yards rushing in the first half, the Redskins finished with 141.

Washington now moves into the hardest stretch of its schedule. The Redskins play four straight road games, beginning next Sunday afternoon in St. Louis. Following are contests at Atlanta, Philadelphia and Cleveland.