Injuries will force the Redskins to start four new players on defense against San Francisco Sunday, including veteran linebacker Brad Dusek and tackle Wilbur Young, both of whom will be activated from the injured reserve list today.

Young, who has been out with a sore right shoulder, will make his Redskin debut in place of Perry Brooks, who has a broken thumb. Brooks may see part-time duty.

Dusek, who is coming back from a dislocated left shoulder, will take over for rookie Mel Kaufman, who has been playing despite a sore knee. Kaufman had been starting for Monte Coleman, who is recovering from a fractured shoulder.

Rookie Dexter Manley will be the starting right end in place of Mat Mendenhall, who aggravated an already-sore knee getting out of his car Thursday night. And veteran Jeris White will spell cornerback Lemar Parrish, who remains hampered with a weak knee. Parrish may be used on nickel-defense situations, however.

"I've never seen anything like this as a player or as a coach," Richie Petitbon, defensive coordinator, said. "We're down to bare bones right now. There aren't many people left to fill in if anyone else goes down."

Joe Bugel, the offensive line coach, received a pleasant surprise yesterday when guard Russ Grimm performed well during an afternoon workout. Grimm had minor knee surgery 12 days ago and had been expected to play only in emergencies Sunday. But Bugel now thinks Grimm could start.

"We'll have to see how he looks in the warmups, but either he or Ron Saul will go," Bugel said. "Russ is one tough guy. He wants to play and I don't believe in keeping a guy back just because he's been hurt. He had earned the spot and we want him in there.

"It'll mean we'll be starting just about all rookies up there, but I'm anxious to see what they can do. I really am."

Said Grimm: "We're 0-4, so I have to play. What good is it going to do me to sit? If we were winning, maybe you could rest, but not in this situation."

The other line starters are rookies Joe Jacoby and Mark May at tackle, first-year player Melvin Jones at guard and second-year man Jeff Bostic at center.

Neither Young nor Dusek has played this season, but their presence could lend some stability to the defensive unit, which ranks second in the NFC despite its injury problems.

"Wilbur could make up some of that pass rushing void we lost when Coy (Bacon) left," Petitbon said. "Wilbur is in much better shape now than he was in training camp, his weight is down (289) and he's looked decent in practice this week. He may not be able to play all the way, but Perry can come in and spell him."

Young, acquired in the offseason from San Diego to bolster the Redskin pass rush, had not earned a starting position when he hurt his shoulder near the end of training camp. But at 6-foot-9 and 289, he is an imposing force who gives Washington added quickness at the tackle spot.

Manley also has fine pass-rushing instincts, although the rookie from Oklahoma State has struggled to pick up the nuances of the Redskin defensive scheme.

Without Mendenhall, however, the Redskins' rush defense will be weakened. As a starter the last two weeks, Mendenhall was excellent against the run, settling down the entire unit in that area.

Dusek is not yet at full strength, and he isn't sure how much he can play. "I'm anxious to see what happens," he said. "I'm sure I'll be a little rusty, but I felt good in practice all week. It will be a matter of seeing how far I can go. I'm nearing full speed, which is encouraging."

The Redskins would prefer to work Dusek in gradually, but Coleman's absence has changed their thinking. Kaufman played well enough the last few weeks, however, to continue as the nickel linebacker.

"Mel has developed enough so he can help us when he's out there," Petitbon said. "It's a much better situation now than a few weeks ago. Mel has experience and we have confidence in him. But Brad gives us a boost both in leadership and experience. We've missed him."

Parrish tried to play despite his weak knee Sunday against Philadelphia and was beaten for a touchdown pass. He has not practiced all week, and Petitbon said he would like to "give him as much rest as possible. I think he can hold up as a nickel back, but we'll have to see about that."

San Francisco is a pass-oriented team, which would make Parrish's loss especially damaging to Washington. If he doesn't play, either Mike Nelms or Trent Bryant would be the nickel back.

San Francisco acquired lineman Fred Dean from San Diego yesterday but could not agree on contract terms. He will not play Sunday, the 49ers said . . . Coach Joe Gibbs said tackle George Starke will be fitted with a new cast today and could be available for emergencies Sunday despite a broken right hand.