If ever there is a week for the Redskins to ambush the U.S. Cowboys in Dallas, this is it. America's Team is more vulnerable than much of America realizes, in a predicament where an injury to one seemingly minor player causes problems at two major positions.

The cowboys are 9-point favorites, so the obvious intrigue is not how they can win their divisional championship for the 11th time but how they could lose it to a collection of Clarence Olkewiczes.

Frequently, the worst pregame exercise for fans, coaches and players is thinking. Impeccable logic and exquisitely conceived game plans all of a sudden become meaningless when a tipped pass ends up as a touchdown or Harvey Martin decides to swallow Joe Theismann before halftime.

Still, when was the last time the Cowboys were giving on-the-job training to most of the left side of their defense? Not just the line, but the line-backer and the cornerback. And also the strong safety.

The defense Tom Landry devised a generation ago is said to be only slightly less complex than the H-bomb -- and nearly as explosive when all the parts fit and are properly activated. Doomsday was quite proper at one time.

But not this week. The left end, John Dutton, will be a starter for just the fourth game. Linebacker Mike Hegman will be in his third week replacing the exiled Hollywood Henderson -- and fresh from being beaten badly for a touchdown by Wilbet Montgomery Saturday in Philadelphia.

Randy Hughes is the reason for the other troubles. His shoulder injury means the regular left cornerback Benny Barnes, probably will open at strong safety and rookie Aaron Mitchell will trot off the bench and play left corner.

A season-ending injury to Charlie Waters elevated Hughes to starter status. He is a fine player, so his injury created problems only when the Cowboys went to a five-back ("nickel" for the NFL junkies) defense.

The ultimate ramifications of the Hughes shoulder separation might be a new defensive team called the "plug nickel." The fifth back night be Landry himself. Or one of the Cowboy cheerleaders, who at least could offer a distraction, the ultimate decoy, making one pass while another is in the air.

Dallas survived the Hughes injury in the fourth quarter against Philadelphia. Which is mainly why free safety Cliff Harris became so emotional after the game. He knows how important coordination and discipline are to the cowboy defense.

He also knows how innovative Landry can be, how adept he is at hiding weaknesses. The Eagles insisted Dallas had 12 men on the field for one important play during their last-drive failure Saturday.

Will Dallas use the 4-3-5 defense again Sunday?

Harris, recalling what makes this rivalry so special wants more than victory against Washington. "I want to knock 'em out," he said.

For that, the Cowboys offer something different from when they lost to the Redskins a month ago in RFK Stadium. The offense is trying to use muscle instead of mirrors now.

After losing four of five games, the Dallas minds decided to perform surgery on the offensive playbook. They did an efficiency study of the prior games, and ripped out between 15 and 20 plays.

"Some of the plays we'd run 20 times for an average of one yard," said offensive left tackle Pat Donovan. "No sense using something that hasn't worked. Like that roll-draw (Jim) Zorn uses in Seattle.

"Nobody else in the league can execute that, but all of us spent four weeks working on it. Throwing out the bad plays means practices are better, because you're working on things that'll probably gain yardage four and five times instead of once or twice.

"So that execution will be better. We still have the finesse plays, the trick stuff. But we're setting it up with basics instead of the other way around."

The Cowboys are running fewer plays, but running them more often. Which halfback will be the primary carrier against the Redskins is the prime question. The one they may secretly hope plays Sunday is Tony Dorsett.

Dorsett is one of the glamor runners in the league, swift and strong. But in his three years against Washington his longest run from scrimmage has been 11 yards. He did not catch a pass until the loss here this season.

Dallas hints his shoulder injury might mend in time for him to play Sunday. His backup, rookie Ron Springs, is not as flashy, although he throws a left-handed option pass, but might have better luck against the Redskins.

Two numbers suggest both teams are less than awesome. The Cowboys have turned the ball over nine more times than they have taken it; the Redskins have surrendered nearly 200 more yards than they have gained.

"We're finally getting some breaks," Donovan said. One of them was his recovering a Scott Laidlaw fumble Saturday during the Dallas drive for the winning touchdown. He laughed and recalled what Landry said after he'd recovered his last fumble:

"Men who recover fumbles usually have been standing around doing nothing."