Critics of the Washington Redskins' one-running-back formation continue to pop up now and then, claiming that the team's rushing would improve if Joe Washington and John Riggins lined up together.

Addressing himself to such criticism, Coach Joe Gibbs said yesterday that the one-back system best suits his team's personnel and is more productive.

"I'm certainly more convinced after the way John and Joe performed last week," Gibbs said. This was before learning that the Redskins are the only team in the NFC with two running backs who have gained more than 600 yards this season.

Washington, despite missing much time because of injuries, has rushed for 747 yards, Riggins, 607. A rested Riggins gained 61 yards on 11 carries in the second half Sunday against Philadelphia after Washington, still suffering from sore ribs, had gained most of his 54 yards in the first half.

"It really works out well," Washington said. "John and I can spell each other and we don't get overworked . . . I like running from this formation."

Washington said the single-man backfield doesn't hurt his receiving. He has caught a team-leading 61 passes for 478 yards. "The only negative factor -- if there is one," Washington said, "is that the opposition knows 90 or 95 percent of the time who will carry the ball on running plays."

Gibbs, who prefers using two tight ends, implemented the one-back formation in the third game of the season, against St. Louis. Since then, Washington or Riggins has been the primary running back for at least one half.

It is more than a coincidence, Gibbs said, that the Redskins' offense immediately began to improve. "We've had days when John has been hot or Joe has been hot," Gibbs said. "Joe had a great day against Detroit, John against Chicago. Joe ran well against Dallas, John was effective against Philadelphia last week.

"I still think the system is right. We could make another decision somewhere down the line. But for now, I like it. John probably should have gone in earlier against Philadelphia, but . . . "

Quarterback Joe Theismann also is in favor of the formation.

"At the start, we were using two backs and didn't get the production we're getting now," Theismann said. "It was an astute move on Joe Gibbs' part. It made us a better football team.

"Of course, we were hurting ourselves early in the season with mistakes. We could have made the two-back system work if we had stopped hurting ourselves. We use two backs some now, but I'm in favor of whatever has been successful. The offensive line's health and maturity have been a major factor, too."

Using one back allows Gibbs to use the second tight end. And production is up there, as well. Even with Rich Caster injured the last few weeks, the Redskin tight ends have caught 45 passes this season.

The Redskins' next opponent, the Baltimore Colts, almost always use the two-back system, with Curtis Dickey and Randy McMillan. However, Baltimore's main concern now is the status of quarterback Bert Jones.

A spokesman for the Colts said that Jones, sidelined last week by a sore right shoulder, threw lightly yesterday and is probable for Sunday's game.

"He's still one of the most talented players I've seen," Gibbs said. "We're expecting him to start."