With Perry Brooks unable to play again for perhaps a month because of a strained left knee, the Washington Redskins will start inexperienced Darryl Grant at right defensive tackle Sunday against St. Louis.

Grant is playing his first pro season on defense after being drafted two years ago as a guard and kick snapper. He was switched to defensive tackle last spring after Coach Joe Gibbs became convinced his aggressiveness on special teams could be utilized at a new position.

"Darryl has come along steadily since training camp, but he lacks playing time," said Torgy Torgeson, the defensive line coach. "We're confident he can do the job, but the only way to find out is to have him play.

"I've been holding my breath all year about that position, because we don't have much depth there. It's a tough place to have an injury."

Brooks hurt his leg on the first defensive play against the Dallas Cowboys Sunday, although he returned to play most of the game. He also has a hairline fracture, but the more serious injury is the ligament strain.

Grant, 6 feet 2, 265 pounds, has replaced Brooks occasionally this season, but has played more as a nose guard in three-man fronts. The Redskins now do not have a reserve tackle, although starting end Mat Mendenhall has practiced at that position and veteran Tony McGee, a backup end, began his pro career as a tackle.

The Redskins probably will sign a free agent. One possibility is Pat Ogrin, who was cut in training camp but is familiar with the system. Also to be decided is whether to put Brooks on injured reserve, which would keep him out a minimum of four games.

"This is like last year, where inexperienced people stepped in and we benefited from it eventually," Gibbs said. "Darryl just has to do the job, that's all there is to it."

Brooks' injury, the Redskins' first serious one since the season started, was the most visible reminder yesterday of the 24-10 loss to Dallas that knocked them from sole possession of the lead in the National Football Conference.

Gibbs, concerned about a second straight inconsistent performance from his offense, said improvement was needed in the running game, which has fizzled the last two weeks.

"The running game is the key to correcting our inconsistency," he said. "We've got to get to where we are rushing the ball well again. The thing about our team is that, when we were playing well at the end of last season, we were averaging around 150 yards rushing a game. The last few weeks we haven't done well rushing the ball. We've left the defense on the field too long, we haven't had the time of possession we want."

The Redskins rushed for 66 yards against Dallas and 61 against Philadelphia the previous week. In each game, they left themselves, too often, with too many yards to gain on second and third downs to suit Gibbs.

"We're putting too much pressure on our passing game," said Gibbs, who indicated that Joe Washington and John Riggins would begin sharing time more equally at running back, although Riggins will continue to start.

Despite his third straight loss to the Cowboys, Gibbs believes the Redskins are closing the gap between the teams. But he admitted his team would have to do a better job handling defensive pressure before breaking a six-game losing streak to Dallas.

"Of the seven sacks we gave up, only three were the fault of the line," he said. "Two came off blitzes we hadn't seen before and two were from breakdowns by a back or a receiver on blocking. Really, I felt like our line had an excellent effort. You can make a line look bad when your backs, quarterbacks and receivers aren't doing a good job.

"I liked what we were trying to get done . . . We had seven or eight times where we just missed a big play. We weren't getting it done, that's all. We have to hit what's there and we didn't. Our outside receivers and quarterback have to make those shots."

Gibbs all but invited the Cowboys to blitz frequently the next time the teams play.

"Hey, I don't mind playing Dallas again if they blitz," he said. "If they do, we'll take our shots. That style of team, we're geared for it. We just didn't do what it took to win this game. We just haven't been good enough the last two times we played them to get the plays when they tried to force us.

"They played a lot more man to man this time than we expected, and not many teams are willing to do that. They just feel they can get enough pressure on the quarterback so he won't have time to take advantage of that coverage."

Gibbs lavishly praised the play of his defense against the Cowboys, calling that unit's development the last two weeks the "most exciting thing that has happened to me since I came here."

He said the defense caused to Cowboys to lose yards 11 times, "something we couldn't do last year. We couldn't force the issue. Our rush defense now is as good as I've seen here. The offense just has to do a better job for us to win."

Fullback Otis Wonsley has a neck strain. His status for Sunday won't be determined until the end of the week. If he can't play, the Redskins will have to shuffle their short-yardage personnel, since Wonsley then is the blocking fullback. His absence also would affect the special teams where, along with Grant, he is a standout. It is likely Grant will be relieved of many of his special team chores, leaving a major gap in that area . . . Gibbs said he told punter Jeff Hayes that he has to improve his kicking, but that the Redskins "still had confidence in him. He's our punter, we haven't given that a second thought. Jeff's a really talented guy, he just has to get back into the groove." Hayes is averaging only 34.6 yards a punt.