Joe Theismann isn't the only Redskin to lose his starting job this week.

Veteran Ron McDole, the first-string defensive left end for the last eight years, will be replaced Sunday by Karl Lorch.

McDole, 39, has a string of 148 consecutive games, as a starter and has not missed a game since 1967.

Lorch, 28, a third-year player out of Southern California, has been used frequently this season as a substitute for McDole in passing situations. Redskin Coach Jack Pardee is anxious to improve his pass rush, which has only four sacks in the last three games.

Meanwhile, Billy Kilmer has drawn the starting assignment Sunday at RFK Stadium against San Francisco because, according to several players, the team has lost confidence in Theismann.

And while Pardee continued to play it cozy as to who will start, one player said, "It's obvious it's Kilmer. It has to be. There isn't much confidence left in Joe right now. Billy will settle down the younger guys and the older guys know what they have to do.

"If the change at quarterback doesn't work, then who knows who's next? You just have to go out and do the job."

In another development at Redskin Park, Pardee said he is not counting on running back Mike Thomas for Sunday's game. Thomas, who has an injured ankle, did not practice again yesterday.

"It's doubtful . . . Mike will play," Pardee said. "We've worked Benny (Malone) and Tony (Preen) in there a lot and one of them will probably start."

Clarence Harmon started the last two weeks for the Thomas, but Pardee said Harmon has worked mostly at fullback this week. "We can still use him at halfback, though," Pardee added.

Most of yesterday's practice was devoted to the defense, but when the offense did work, Kilmer got most of the time at quarterback, as he has all week.

"It's the same time it's been all year," Pardee said. "We have two No. 1s and we'll go with either one."

But as some players indicated, they knwo Kilmer is the man now.

"Billy was sharp last week and he's in completely good health now, too," Pardee said. "Joe has done well, too. There have been some mistakes the last couple of weeks, but Joe has done a lot of great things. It just gets back to you need two quarterbacks to win."

In the last two games, teammates say, Theismann started drifting out of the pocket, scrambling, and he was not as patient as he had been through the six victories. More importantly, fewer points were put on the board.

"You never knew where Joe was going to be," on player said. "You know where Billy will be every play. It's just time for him to play."

The Redskins' new wide-open offense seemed to be tailored especially for the mobile Theismann, but Pardee said Kilmer is just as capable of running as Theismann. Pardee conceded that Kilmer is not nearly as mobile or agile, but said, "We don't plan on him having to scramble. We put in one game plan evey week and both quarterbacks work on it."

There is a basic difference in the styles of the two quarterbacks. Theismann throws a much harder ball than Kilmer and that takes some getting used to.

Kilmer has thrown only two passes this season and completed one - six weeks ago in St. Louis against the Cardinals. The competition was for two yards to wide receiver John McDaniel.

Kilmer, in fact, will be throwing to only one wide receiver he has had game experience with - Danny Buggs. The other three - McDaniel, Ricky Thompson and Terry Anderson - were not with the Redskins last season.

"There isn't all that much difference," Buggs said. "Timing is the big thing and we've been working a lot on this after practice. Even when Joe was starting, Billy would stay after and work with us, and now that Billy is starting, Joe is doing the same thing."

Tight end Jean Fugett and tackle Terry Hermeling practiced yesterday, but were not at full speed. Hermeling, with a sore knee, said he expects to play, while Fugett, who had a cyst behind his knee drained Wednesday, is not certain he will be ready.