George Allen gave his battered football team a rare day off from practice yesterday and some depth at fullback by signing former Cardinal running back Eddie Moss.

Cut by the Redskins late in the preseason, Moss was one of three veteran NFL running backs given tryouts by Allen and his coaches earlier in the day. Harold Hart, a former Oakland Raider also cut by the Redskins in training camp, and Jeff Kinney, who once started for the Kansas City Chiefs, also worked out in the morning.

Moss won out, mostly because he had spent a good part of the summer with the Redskins and would ahve little difficulty picking up the system.

Allen said his decision not to place fullback John Riggins on the injured reserve list was based on a diagnosis by team physician Stanford Lavine that Riggins might be physically ready late in the season.

Riggins was fitted with a cast yesterday and he is expected to wear it at least three weeks. His injury has been diagnosed as a tear of the medial colleteral ligament in the right knee, and there is some hope that an extensive rehabiliation program may allow Riggins to return within six to eight weeks.

"I really have no idea on that," Allen said. "But John might be a fast healer. he's tough, and he might surprise them all and come back sooner. I'll take that chance because he wants to come back and he wants to play."

Allen also admitted yesterday that he is becoming increasingly concerned over Pat Fischer's back injury. He said Fischer has been seeing a specialist. "We're supposed to get another diagnosis this week.

"The big thing is how Pat feels," Allen said. "He said he thought he could play against Dallas, but if a player doesn't practice, I hesitate to put him in. Hopefully this week he'll be able to practice and play."

Privately, other team sources say that Fischer's physical condition is probably not going to improve much. No one knows how long he will be able to stay in a game even if the does get back into the starting lineup.

The length of time it takes for Fischer's back to recover from the pounding of a game is also a major concern. Fischer has missed two games since he started against the Cardinals, although he was able to practice late last week.

Rookie Clarence Harmon will attend every workout, and probably a few extra meetings, this week. He is expected to take over for Riggins and Bob Brunet.

Brunet suffered a contusion of the spinal cord against the Cowboys and was placed on the injured reserve list yesterday, making room for Moss.

"I hate the conditions that are giving me a chance to play," Harmon said yesterday. "You hate to see anyone injured like that, especially those two guys.

"Yeah, going in there was kind of scary. I was nervous because I had been off for two weeks (with a sprained ankle) and I hadn't been hit. But after the first two licks, it all felt pretty good.

"When I came into the huddle, Billy (Kilmer) said, 'You're all right, you can do it.' Then we had a time-out and they were all encouraging me.

"I felt pretty good after I got seven yards my first carry. I wasn't thinking about fumbling or anything like that. All I was worried about was the blocking."

In addition to gaining 38 yards in seven carries, Harmon, who weighs only 195 pounds, scored his first NFL touchdown on a one-yard pass from Joe Theismann late in the first half.

The Redskins also say that Calvin Hill will be worked at fullback, althrough the addition of Moss, a 6-foot, 215-pounder who played in St. Louis last year, will give the Redskins enough depth at the position for now. Moss, 29 and a four-year veteran, also is a good special teamer.

During the Cowboy game, Hill was studying fullback plays on the sideline in case Harmon could not continue.

"I could handle it," Hill said yesterday. "I think it would be kind of fun, and I also thought Clarence did a heck of a job. The kid can play.

"I played fullback once in the pros - in the Pro Bowl of 1975. We had guys like (Terry) Metcalf, (Lawrence) McCutcheon, and (Chuck) Foreman, and me, of course. Actually, I volunteered.

"I carried the ball twice. One time, I ran right over the quarterback, Jim Hart. I thought I was supposed to go straight. He thought I was rolling out. I hit him right in the eye and he had to leave the game. So James Harris came in and won the MVP trophy. I told him I should have gotten a piece of it."

Chris Hanburger jogged a few laps around the track yesterday, limping noticeably, and Allen repeated he probably will not play against the Giants. Hanburger also has a torn kee ligament, not nearly as severe as Riggins' . . . Offensive coordinator Charley Waller said he thought Kilmer would be able to practice today and play Sunday against the Giants, despite his bruised left shoulder . . . Allen said he hoped cancellation of practice "might give them a lift. We've got a lot of bumps and bruises. That's for this week only." . . . The Redskins are ninth in total offense in the NFC, seventh rushing and 10th passing. They are 10th in total defense, sixth against the run, 11th against the pass.