Defensive Coordinator Richie Petitbon has run out of patience. He has waited through six weeks of training camp for the Redskin front four to improve, and it hasn't.

If the situation doesn't change during Saturday night's preseason game against the Baltimore Colts (0-2) in Baltimore, he is almost certain to make some significant personnel adjustments that could affect such veterans as Perry Brooks and former Colt Fred Cook.

"We've been treading water except for Dave Butz and Karl Lorch," said Petitbon, reflecting Coach Joe Gibbs' belief that the defensive line is "still a total mystery."

Said Petitbon: "We've got to get some answers right now. We can't go on this way. We got a lot of players but no one seems to be breaking out of the pack. I hope that will change Saturday."

Petitbon and Torgy Torgeson, line coach, will particularly be watching four players during the 8 o'clock contest (WMAL-Radio-630, life; WMAR-TV-2, 11:30 p.m., taped; WJLA-TV-7, Sunday at 8 p.m., taped):

Cook, the former Colt end making his first appearance in Memorial Stadium since being traded to Washington.

Brooks, who is in danger of losing his starting tackle job for the second straight season.

End Mat Mendenhall, who will be playing in his first preseason game after recovering from an early-camp knee injury.

Tackle Wilbur Young, the former San Diego Charger whose play against the run has not matched his pass-rushing standards.

Cook and Brooks could have their Redskin futures determined in this game. Neither has had the type of preseason the Redskins were projecting, so they both need to play well.

The Redskins are hoping that Cook, who asked to be traded by Baltimore because he was not happy there last season, is hoping to regain his once exceptional form against his former teammates. To help, Torgeson has switched Cook from the right side back to the left, where he played with the Colts.

Cook, according to Petitbon, "really has not shown the type of consistency we were hoping for. He's been playing like he's got it (the roster) made. That's a bad assumption on his part. The way he's been playing just isn't good enough. You have to figure he'll be fired up against his old team. If he isn't, that will tell us something."

Brooks, the starting right tackle throughout camp, was included in Petitbon's blanket statement that "we need someone who can play right tackle against the run. Right now, no one is doing a decent job against the run.

"Wilbur has shown excellent pass-rush moves from right tackle and he's going to help us there, he really is. But he hasn't shown much against the run. He's finding it difficult to play in our disciplined system. a

"Perry has to take on the blockers stronger and not get blown off the line. He's playing too softly. We've talked to him about it but he hasn't shown much improvement."

Petitbon's flexibility will be determined, in part, by how well Mendenhall does at Coy Bacon's right end spot. Mendenhall just began practicing Monday after missing three weeks, but has shown surprisingly well in workouts. If he could hold up on the early downs against the run, that would allow Bacon to become a pass-rush specialist on later downs.

Bacon appears to be closing in on a roster spot, which would be surprise. He has been helped by Mendenhall's absence and Cook's inconsistency. And Petitbon says Bacon has "come on and played pretty well the last week. He was too heavy (277) but now he's down to 270 and has promised me he'll be 265. If that's true, he can play."

Early in camp, the Redskins were figuring that Mendenhall would step in as the starting right end with Cook and rookie Dexter Manley, who should survive the final cuts, as the pass rushers from the outside, making Bacon expendable. And Young would replace Brooks at tackle to team with Butz. So far, nothing has worked out as planned.

Young has improved after losing weight and still may wind up as a starter. However, Cook, who left Baltimore a bitter man, agrees that he hasn't played well.

"I appreciate that the Redskins have been so patient," said Cook, who is always upbeat. "My attitude hasn't been the greatest. I hadn't realized how depressed I was, how much last year took out of me. I wasn't even sure I would play again. I wasn't in the best shape when I reported, either."

The Redskins probably will keep seven defensive linemen out of the nine currently on the roster. Still also in contention is first-year tackle Pat Ogrin, who Petitbon says probably is behind due to a year's layoff from a knee injury.

This will be Washington's first road game under Gibbs. The Redskins have won their first two contests at home. Baltimore has lost its first two games, to New Orleans and the New York Giants, on the road.

The Colts also are a rebuilding team, with five offensive striking power supplied by quarterback Bert Jones, running backs Curtis Dickey and rookie Randy McMillan and receivers Roger Carr and Ray Butler. Their defense has been strengthened by the addition of end Donnell Thompson, who should provide a challenge for the Redskins' ailing offensive line.

That line will be using Darryl Grant at guard in place of the injured Melvin Jones, giving Washington three rookies in the starting five spots. "I worry about that, and I worry about us keeping up our tempo and playing hard," said Gibbs, who will play quarterback Joe Theismann for about one-third the game. "If we let down, that's when all the trouble begins."