Billy Kilmer's latest physical woe - a sore back - replace Mike Thomas' hamstring as the Redskins' main concern in their continued preparations yesterday for Sunday's season opener.

Kilmer, already limping with a chronically sore knee, appeared to be in discomfort as he hobbled around the field yesterday. No one in the organization would say what ailed Kilmer, but reliable sources indicated his back has been hurting the last few days.

A reporter asked Kilmer is his knee was acting up and he said "No, definitely not." When asked what was wrong, he said he had no comment.

Redskin coach George Allen also sidestepped the issue when asked why quaterback Joe Theismann handled most of the work in yesterday's 2 1/2 hour practice. "Well," said Allen, "Billy took quite a bit of it the other day, and we wanted to give Joe some more work."

Kilmer participated in the drills yesterday and seemed to be throwing the ball with zip. But he was hobbling noticeably as he dropped back after taking center snaps.

Kilmer's name did not appear on the injury report the Redskins sent to the FNL office Tuesday. Team sources said they expect Kilmer to start Sunday - as long as his back doesn't get worse.

But Kilmer's latest problems once again points up the fact that the veteran quarterback, at 38, is more vulnerable than ever to nagging injuries.

Thomas was able to participate in his first full practice since before the New England game two weeks ago, and said his sore left leg is the "best it's felt since I first got hurt in training camp."

"I feel a whole lot better about it. I haven't felt this good in a long time. I can smile after walking off the practice field, and it's been a long time since I could say that."

Thomas said he did not try and go all out, simply as a precaution, and that he tried to avoid sharp cuts. "I didn't try to come out and fly today," he said. "I just want to get it back gradually."

Thomas operated in the same Backfield most of the day with regular fullback John Riggins, a sure indication that Allen would like to start him at tailback Sunday against the Giants. But once again, Allen was not showing his hand.

"It's still too early to tell," Allen replied when asked if Thomas would start. "This is the first day he's worked. He has made progress, but he didn't go at top speed.I told him to run under control. This is the only way he'll get his confidence and his timing back. But we'll see how he is tomorrow." "I don't feel like it's 100 per cent yet," Thomas said, "but I'm sure I can play. I don't know what their plans are for me, but I should be alredy. I know I want to play. It'll be up to the them."

Even if he starts, Thomas likely will not play the full game. He carried the ball only three times in preseason games, and yesterday's practice was only this sixth full workout since he pulled up lame the day he reported to training camp

Meanwhile, center Len Hauss, for the first time in as long as anyone could remember, actually missed a full practice session.

He had his puffy left knee drained Tuesday night by team physician Stanford Lavine and Allen said he was held out yesterday mostly as a precaution.

Hauss probably will return to workouts today, and play in his 183d consecutive game Sunday, the 175the straight time he will have started at center on the Redskins offensive line.

But linebacker Chris Hanburger's streak of 135 consecutive games will end. The all-pro outside linebacker spent another day in Arlington Hospital yesterday, still undergoing tests to determine what caused the suspected infection following his appendectomy Sept. 1.

A spokesman in the office of surgeon Frank Cardenas said Hanburger was "doing quite well" yesterday and that he still may play against Atlanta next week. "It's just very difficult to say right now, we'll know more about it later in the week," he said.