Middle linebacker Neal Olkewicz, the Redskins' leading tackler and most consistent defensive player this season, will not be able to play in Sunday's game here against Baltimore and, probably, the last game of the season, in Los Angeles, because of strained ligaments in his right knee.

Olkewicz hurt the knee on the last play of the first quarter against Philadelphia Sunday but returned to the field after missing one play and was credited with 15 tackles. He will be examined again today by team physican Stanford Lavine.

"He's definitely out this week and I have to think he won't play the next week, either," Coach Joe Gibbs said. "I'd be shocked if he was able to come back. But he's a gutty guy. How else could he have played all that time against Philadelphia with a bad leg?"

Olkewicz will be replaced by Pete Cronan, a midseason waiver acquisition from Seattle who has been a special teams standout here. Cronan, a 1977 second-round pick, did not play in 1980 because of a neck injury. He has started three games in his career.

The loss of Olkewicz, who has 187 tackles this year, is a severe blow to a defense that has been struggling to stop opponents' running backs. Olkewicz had been the Redskins' one front-line linebacker who had not missed a game this season because of an injury.

Gibbs also said, when asked, that he erred in not playing fullback John Riggins more against the Eagles. Riggins was not used until the second series of the third quarter, then gained 61 yards in 11 carries to become the Redskins' most effective runner in the game.

"John had a slight hamstring pull and didn't get as much work as usual during the week before the game and Joe (Washington) was playing so well the last few weeks," Gibbs said. "My gut feeling going in was that our best chances were to go with Joe.

"You go in with certain feelings that you want to head in a particular direction and you see how that goes. I guess you could say, in this case, my gut feeling was wrong."

With the Redskins using a one-back offense, Gibbs has a continual dilemma involving Washington and Riggins. How does he give each adequate playing time, yet make the most use of Washington, his quickest runner, leading yard gainer and top receiver?

"Joe does so much that you have to have him in there," Gibbs said. "But John is good, too. The one-back offense has been good to us and we are going to stay with it, but you want to have both of them complement each other. They have contrasting styles that should work to our benefit."

Washington will continue to start and do most of the running because the coaches feel a quick back functions best in this offense. But, Gibbs said, he would like to increase Riggins' workload, which has fallen off substantially in the three games since he gained 82 yards on 26 carries against the Giants.

Riggins has run the ball only 26 times since then, picking up 79 yards. And until Sunday's second half, most of those carries were on short-yardage and goal-line plays.

"We normally give each of them a good shot in every game, but we haven't done that recently with John," Gibbs said. "Sunday, John ran as well outside as I've seen him do all year, and that's normally what Joe does best. It should be a perfect setup for us, with Joe starting and John coming on as a pinch hitter."

For the season, Washington has 176 carries for 747 yards (4.2 average) and Riggins has 173 carries for 607 yards (3.5).

Gibbs also said:

* The special teams, which shut down a good Eagle return game, are "playing by far the best of any of the units right now. They are dominant. The last five or six weeks, they've been great."

* He was far from satisfied with the offensive performance Sunday, especially the dropped passes. They were an early season problem that has reoccurred the last three weeks.

Virgil Seay, who dropped two passes Sunday and one in the end zone the week before, was replaced for most of the second half by Ricky Thompson. Gibbs said that Alvin Garrett, signed off waivers two weeks ago, could play more against Baltimore at that wide receiver position.

* He believes the team has played "good football" the last nine weeks (6-3 record) and he doesn't think anyone in the league "can manhandle us" now. But he said the Redskins' inability to score a lot against good teams, while also giving up a substantial number of yards, "forces me to be realistic about where we are."

* The team would become better if players on injured reserve such as Rich Caster, Clarence Harmon, Fred Dean, Mike Clark, Charlie Weaver, Wilbur Jackson, Charlie Brown, Larry Kubin and Cris Crissy could be activated.