Early in the season, when Joe Washington was sidelined with a sprained ankle and John Riggins couldn't play because of a sore knee, Redskin Coach Joe Gibbs decided to go to a two-tight end, one-running back formation.

That one running back was Wilbur Jackson.

Jackson gained 104 yards on 22 carries against St. Louis in the first game the formation was used 10 weeks ago. He picked up 64 yards on 17 carries in the first half against the Philadelphia Eagles the following week.

Barely a whimper has been heard from Jackson since.

He injured his left knee that game, sat out five games, reinjured it the one time he tried to play since, and has been on the injured reserve list the past three weeks.

Meanwhile, Washington and Riggins have prospered with the new system while all Jackson can do is watch. What looked like possibly his best season ever has turned into a major disappointment.

Jackson isn't one to brood.

He says the Redskins were as patient as they could have been waiting for his knee to come around and the whole situation "is just the breaks of the game. Who's to say what I might have done if I hadn't been hurt?"

At first, the injury wasn't believed to be serious and it was thought Jackson would be out only two to three weeks.

The injury was diagnosed as stretched ligaments and the Redskin physicians felt no surgery was necessary.

Jackson said he suffered the injury when he fell hard on the artificial surface in Philadelphia.

"Even after looking at the films, I couldn't see where anybody twisted my knee or gave me a hard shot," Jackson said. "I just hit the ground hard and my knee somehow got twisted."

Finally, five weeks after the initial injury, Jackson felt well enough to test the knee against Detroit.

He ran back two kickoffs and blocked on another.

He said he never got hit on the knee, but it was very painful. "It just wasn't right," he said.

The Redskins could wait no longer, so Jackson was put on the injured list.

"They gave me the time to get well, but I just couldn't get the knee to come around," Jackson said yesterday as his teammates prepared for Sunday's game at Buffalo. "I told the coaches that I could only play in certain situations, so they made the decision to put me on the injured list. They had no choice."

The knee feels better now, Jackson said, but the Redskins already have used their three in-season roster moves, so the only way Jackson can rejoin the team, without having to go through waivers, is if the Redskins make the playoffs.

"We wanted to keep him active if at all possible, so we waited as long as we could," said Gibbs. "We were told originally that he'd be out only two or three weeks so we decided to wait it out. Once it didn't get any better, though, there wasn't anything we could do but put him on the injured list."

Gibbs said that once the decision was made to go to the one-back alignment, Jackson "made it pay off right away. He did his job."

Joe Washington went through the full workout again yesterday morning and now looks like the probable starter in Buffalo in spite of his torn rib cartilage . . . The Bills are third in the entire National Football League in offense, averaging 377 yards a game.