Redskin linebacker Brad Dusek underwent surgery yesterday at Sibley Memorial Hospital to repair a ruptured disk in his back.

Although a team spokesman said it was too soon to tell if Dusek would be able to play again, General Manager Bobby Beathard said, "We have to proceed from now on with the idea that Brad won't be able to play this season. It's the only sensible approach to take. That way, it will be a bonus if he returns, and I really hope he can."

The operation was performed by Dr. Bruce Ammerman. Dusek is expected to leave the hospital within a week to begin rehabilitation.

The surgery lasted "a couple of hours," according to Ammerman. "It went fine."

The doctor would not predict when Dusek could begin preparing for the 1981 season. But he did say, "We are cautiously optimistic he will do nicely."

Dusek, an eight-year Redskin, first complained of back pain following a three-day mimicamp that ended 11 days ago. He was admitted to Sibley last week and was put in traction, but that treatment proved unsuccessful.

With Dusek's status uncertain, the Redskins now find their linebacking corps severely depleted. They have three healthy linebackers: Rich Milot, Neal Olkewicz and Monte Coleman.

Milot will be moved from his role as backup to middle linebacker Olkewicz in order to take over Dusek's position on the left outside. Defensive Coordinator Richie Petitbon had wanted to keep Milot in the middle, where he proved especially capable defending against passes.

The Redskins finished last season with five linebackers. Then veteran Pete Wysocki retired during the winter. Coach Joe Gibbs says he wants to carry six linebackers this year, one of whom probably will be Dallas Hickman, who also is a defensive lineman.

Gibbs and Bobby Beathard believe that their starting linebacker group is competent even with the loss of Dusek. But they are sure to use the upcoming draft to add depth.

"We hope to pick up some linebackers in the draft," Beathard said. "This certainly becomes an important spot for us to fix up. We just have to go about it in an intelligent way."

Dusek was considered the team's best linebacker and had gained a reputation for his quiet but efficient style of play.