Washington Redskins Coach Joe Gibbs said yesterday his favorite six-shooter, fullback John Riggins, will start against the Dallas Cowboys in the season opener Monday night at Texas Stadium.

Gibbs' choice seemed to surprise some at Redskin Park, who had figured that George Rogers might start in the one-back offense. Some had figured that Riggins, who at 36 is the oldest running back in the league, has practiced only 22 days since ending his holdout and that he might need more time to ready his back and hip for the inevitable pounding.

Don Breaux, the running backs coach, said that it is "very likely" that Rogers will spell Riggins on every third or fourth series against Dallas. This pattern would be similar to the way the since-traded Joe Washington often spelled Riggins the past few years.

Breaux emphasized, however, that the game plan isn't definite. Of course, he noted, "You can't dispel what Riggins has done in the past against Dallas."

Riggins has done plenty against Dallas, dating back to the conference title game of the 1982 season, which opened the door to the Redskins' Super Bowl victory. It is for this reason, combined with Gibbs' belief in Riggins and his production, that others fully expected Riggins to start.

Riggins ran for 165 yards and 111 yards to generate two victories over the Cowboys last year. Including that NFC title game in January 1983, he has averaged 29 carries for 119 yards in his last five games against Dallas.

"John's been back there so much for us," Gibbs said. "He's led us all the time. There's a lot of factors to be considered. We want to see if we can make both John and George happy. George probably will be in there right away."

Neither Riggins nor Rogers, 26, seemed outwardly affected by the season-opening depth chart. Said Riggins: "I'm gonna get my four at bats. It doesn't matter whether I bat leadoff or cleanup."

Rogers said: "John's been here longer than me, so he should go ahead of me. He won't hurt the team any, that's for sure. I don't have any gripes. I kind of figured he would start.

"John's getting paid an awful lot of money to play behind me. I didn't have a good preseason. I fumbled a lot and he held onto the ball. It's not going to be a strain. I'll get my shot."

On the phone from Dallas, Cowboys Coach Tom Landry said: "I expected it, because Riggins is really grooved into Washington's attack. I'm sure Rogers is still learning."

Gibbs did not want to make a scene over this. Before yesterday's afternoon workout, he gave a noncommital response to the Riggins-Rogers questions: "Both of them will have their tongues hanging out by the end of the (Dallas) game."

The reporter's response: "Whose tongue will be hanging out first?"

Gibbs laughed. "John's will." Some grand announcement, huh?

Rogers rushed for a team-high 142 yards on 36 carries during the preseason. He fumbled three times. "You know what happens to Coach Gibbs when a guy fumbles," said tackle Mark May. "Goes nuts."

Riggins' preseason numbers were mundane: 13 carries for 46 yards. However, in Riggins' first game back, a 37-36 victory over New England, he replaced Rogers for one second-quarter drive, a nine-play, 73-yard job.

On this drive, he rushed five times for 19 yards, including the final two yards for the touchdown. Team doctors said that, so far, he has had little problem with either of the ailments that plagued him most of last season, bursitis in his hips and a sprained lumbar.

Rogers was acquired during the offseason from New Orleans. Over the last four years, he has been the league's fourth most-productive runner with 4,267 yards. He trails Walter Payton, Tony Dorsett and O.J. Anderson. Riggins has rushed for 3,853 yards, sixth-best, fewer than 100 yards behind No. 5 Eric Dickerson.

"When I play, I need to get the ball a lot, just to get started," Rogers said. He was smiling, as always, when he figured a game plan that might please both veteran running backs.

"Say we have 35 carries a game. That's 16 per man and that would be fine," he said, perhaps sounding more accurate philosophically than mathematically.

The Redskins also announced yesterday that veteran pass-rusher Tony McGee has retired. McGee accumulated 115 quarterback sacks in his 14 seasons, but has a bad knee. With his retirement and that of the Rams' Jack Youngblood, only the Raiders' Lyle Alzado and the Patriots' Julius Adams remain from the durable defensive line class of 1971.

It's been a question of age versus youth throughout this preseason for the Redskins. Gone are veterans George Starke, Mark Murphy, Perry Brooks, Mike Nelms, running back Washington and Charlie Brown. The replacements are named Dan McQuaid, Raphel Cherry, Dean Hamel, Gary Clark and Malcolm Barnell and only Barnwell (26) is older than 24.

Of course, veteran Mark Moseley, 37, serves as the keeper of Redskins experience. He shooed away the challenge of Tony Zendejas, who was traded to Houston.

"I guess age won out in this case, too," May said of Riggins' start Monday.