Jim Jeffcoat, the left defensive end of the Dallas Cowboys, said it was the best game he ever had. Well, of course, there was that six-sack game in high school, but that was a long time ago.

Jeffcoat, a 6-foot-5, 263-pound three-year veteran, displayed the speed of a bullet train in getting past Washington left tackle Dan McQuaid in yesterday's 13-7 Cowboys victory at RFK Stadium. He had five sacks of Redskins quarterback Joe Theismann, who completed only 14 of 31 passes for 143 yards and three interceptions, working under heavy pressure throughout the game.

McQuaid, playing in his first full NFL season and replacing injured Joe Jacoby, had such a difficult time with Jeffcoat that the Cowboys' other linemen -- Ed (Too Tall) Jones, John Dutton and Randy White -- were able to try some unplanned stunts on their blockers.

"Jim was handling McQuaid pretty well, so eventually, he and I just stopped stunting and let him go one-on-one," said the 6-7 Jones, who batted down two passes within four plays in a second-quarter series with Dallas leading, 3-0. "That let me and Randy do some stunting with each other."

Two plays after Jones' second knockdown, White swatted down Theismann's pass on fourth and two at the Dallas 37.

Four of Jeffcoat's sacks came in the second half, two on third down. His most important sack, however, resulted in a 13-yard loss on first down with 45 seconds left. Theismann had just completed a 26-yard pass to Art Monk at the Cowboys' 48 as Washington attempted a final, desperation touchdown drive.

"It was undoubtedly the best game I ever had," said Jeffcoat. "I studied my man all week and found some weaknesses that I was able to take advantage of. The Redskins gave him a little blocking help, but basically, it was just one of those days. It was a lot easier than playing against Joe Jacoby. Joe Jacoby is an all-pro."

The Cowboys' defensive unit entered the game under a swirl of controversy after their loss to St. Louis last Monday night. White and Dennis Thurman allegedly had a shouting match on the sidelines during that game and several other players were involved.

Yesterday, the unit was totally in sync as the line created pressure and the secondary had excellent coverage most of the game.

"The Redskins try to nickel-and-dime you most of the time and then look for the big play," said cornerback Everson Walls, who had two interceptions. "But we recovered quickly whenever they did get someone open and it may have frustrated Theismann."

This game, with three turnovers by Washington and none by Dallas, reemphasized the importance of turnovers. Since 1982, Washington is 2-9 in games in which it has had more turnovers than its opponent. It is 35-1 in games it has had fewer turnovers.

Cornerback Ron Fellows, who stopped Washington's opening drive with an interception in the end zone, said the Cowboys played differently yesterday than when they intercepted six passes in the season-opening 44-14 victory over Washington on Sept. 9.

"In the first game, we tried to mix things up a lot more," he said. "In this game, we just showed them what we have and said, 'Beat it.' Today, at least, they couldn't beat it."