The Redskins are expected to obtain Fed Cook, a former standout defenseive end who slumped last season, in a trade with the Baltimore Colts, it was learned today.

Washington apparently will surrender a low draft choice, probably in the seventh to 10th rounds, for Cook, who had demanded to be traded or released by Baltimore. Earlier this week, the Colts waived another former defensive star, tackle Joe Ehrmann, who had interested the Redskins until they traded for San Diego's Wilbur Young.

Cook, 29, is a seven-year veteran. Until last year. when injuries and unhappiness with the Colt coaching staff affected his performance, he had been one of the team's most consistent players and a star on what had been a top AFC defensive line.

He had a team-high 11 sacks in 1979, five in 1978, nine in 1977, 11 in 1976 and 17 in 1975, his second year in the league. He also has led the Colt defensive line in tackles three times and has 12 career fumble recoveries.

The trade would complicate an already muddled defensive end picture for the Redskins and could mean the eventual departure of 37-year-old Coy Bacon, their leading sacker the last three years.

Cook, 6-foot-4 and 252, is expected to compete with Mat Mendenhall, last year's No. 2 draft choice, and rookie Dexter Manley for Bacon's starting position. If Cook regains his previous form, and if Manley and Mendenhall progress the way the coaching staff hopes, there would be no room for Bacon, who irritated Coach Joe Gibbs by missing all three minicamps this spring before signing a one-year contract.

Guard Jeff Williams, the last player to upset the staff, when he reported out of shape to a minicamp, was traded for Young.

Mendenhall, who is coming off a year on the injured reserve list, twisted a knee in practice yesterday and is expected to miss two or three days of workouts.

Mendenhall's leg was caught under a pile of teammates during a live contact drill between the offensive and defensive lines. "It was scary at first," said Gibbs, "because you never know how bad the situation is going to be. But, fortunately, Mat should be okay. You try to limit the injury possibilities during practices but you have to have contact work."

Both Mendenhall and Manley have pleased the coaching staff with their work in this camp, but with Bacon's age and their inexperience, the Redskins apparently have decided they need to add a yound veteran like Cook.

There was no movement in negotiations between the Redskins and No. 1 draft choice Mark May, in his fourth day of a contract holdout. No new talks were scheduled.

Ralph Cindrich, May's attorney, said he was waiting for a call from the Redskins before being able to evaluate his next step in the negotiations. Informed that the Redskins were waiting on him to make the next phone call, he laughed.

"Well, I'm not going to let pride get in the way," he said. "I'll pick up the phone and call to see if we can get something started."

Even without May, the roster at camp continues to grow. Two more veterans, fullback Rickey Claitt and return man Mike Nelms, checked in and participated in both workouts today.