Mat Mendenhall, the Redskins' highly touted second-round draft choice in 1980, and Joe Jacoby, the little-heralded rookie free agent from Louisville, might start their first NFL games, Sunday in St. Louis.

The status of Mendenhall, whose pro career has been marred by injuries, depends on the health of defensive tackle Perry Brooks, who isn't recovering from a strained neck as quickly as the Redskins had anticipated. But Jacoby, strictly a tackle before this week, already has been penciled in to start at the team's troublesome left guard spot.

Richie Petitbon, the defensive coordinator, said that if Brooks can't play Sunday, then Mendenhall would start at left end, and Karl Lorch, who normally plays that spot, would move to Brooks' tackle position.

"I'd say Perry is doubtful right now," Coach Joe Gibbs said. "We have to hope he improves faster than he has. It doesn't look good now, but a few more days could improve the situation. I hope he's at least available for spot duty." Brooks hurt his neck in the Giants game and has not practiced this week.

But even if Brooks does come around by game time, Mendenhall is scheduled to play at least half the defensive plays, and probably more, at Coy Bacon's right end. Bacon continues to be the starter, but Mendenhall played so well against New York last week that the two now share the position.

"Coy's at an age where he needs to be rested; he can't go every play," Petitbon said. "We need to keep him fresh for passing downs. That's what he does best, rush the passer, and that's what we like to have him do with fresh legs. Mat can play the early rushing downs, then we can bring Coy in."

Whether Mendenhall eventually becomes a permanent starter, as had been hoped before training camp, depends on his improvement and Bacon's adjustment to his more specialized duties.

"We're not worried about who starts there," Petitbon said. "We haven't thought about that. We're too nicked up anyway. We just have to hope to get enough players healthy to put out a team."

Injuries have opened up the opportunity for Jacoby, who made the team as a swing tackle but was switched to left guard. Left guards Russ Grimm and Jerry Scanlan are ailing.

"Joe will start Sunday, and we think Russ will be able to play in spots at both guard and center," Joe Bugel, the coach of the offensive line, said. "Jerry will be able to play both guard and tackle."

Grimm tore knee cartilage last Sunday, but an operation has been delayed until he can determine whether the knee will hold up under practice conditions.

"I'm going to give it a try Friday and see how it feels," Grimm said. "Got to give it a test sometime."

Scanlan has neck and shoulder problems that have hindered his consistency. The Redskins would like to give him time to heal, which was one reason they moved Jacoby to guard on Wednesday.

"Joe has really picked up guard very fast," Bugel said. "We knew he had the athletic ability but we didn't know if he could handle the pulling part of it.

"But he's been amazing. He is getting out there and going. He's always shown us that he is a quick learner, which has helped him this week.

"I'm confident he can do the job this week. You got a guy like him who's 6 feet 7 and weighs 295 and see him pulling and going against linebackers, and you have to like it."

The Redskins already have lost two left guards, Fred Dean and Ron Saul, because of injuries. And neither Grimm nor Scanlan have been completely healthy since early in training camp.

Although starting Jacoby is a risk -- he is inexperienced at tackle, much less at this new position -- the Redskins have little choice. But Bugel has been high on Jacoby's versatility almost from the day he first saw him at an early minicamp.

The Redskins also have had equally high hopes for Mendenhall since General Manager Bobby Beathard surprised onlookers by taking the Brigham Young star so early in the 1980 draft.

Mendenhall spent last season on injured reserve recovering from a ruptured appendix. His attempts to win a starting spot in the recent training camp were negated by a early knee injury that didn't heal until the end of the preseason.

"Mat is really coming on; he's finally settling in," Petitbon said. "Last week was the most he's played for us in any game since we drafted him. He's getting more confident and I think he can help us."

Bacon played decently in the first two games, but had only one sack. The Redskins feel he still can be an effective pass rusher, even at age 38, if someone else can take over the early down chores against the run, as Mendenhall is doing.

With Mendenhall and rookies Mike Clark and Dexter Manley, the Redskins suddenly have some young, promising defensive ends. Both Clark and Manley are considered excellent potential pass rushers, but how much they play will depend on Bacon. If Bacon can't mount pressure on the quarterback in his new role, the Redskins could be forced to turn to their youngsters quicker than planned.