The main reason the Los Angeles Rams fired George Allen Sunday was that he persisted in trying to make trades as though he were the general manager, it was reported yesterday.

Aware that Allen's discharge by the Redskins stemmed from his free wheeling deals as vice president and general manager as well as coach, the Rams stipulated when they hited him last Feb. 1 that his duties were restricted to coaching.

An irony of bis downfall in Los Angeles was the displeasure by some in the Ram front office over the trade he advocated for kick returner-defensive back Eddie Brown in light of the criticism the Redskins have received over the deal.

Sources said the trade of Brown prompted the Ram front office to intensify their monitoring of Allen's off-field activities.

Unlike his situation in Washington, where Allen called all the shots on and off the field, his role in acquiring players was to be secondary to owner Rosen bloom and son Steve.

Allen yesterday told The Washington Post he bent over backward in an effort to get along with the Rams front-office staff.

He admitted he was persistent in pushing for help in certain areas, including seeking quarterback Billy Kilmer.

One source said a kick returner of Brown's caliber usually brings No. 2 draft choice, noting the Rams reportedly were unwilling to give up much more than that for kilmer.

The Rams gave up two offensive linemen, Donnie Hickmanand Jeff Williams (who left for the Redskin camp yesterday), a No. 3 draft choice for 1979 and Nos. 2 and 5 for 1980. The Rams, who value high draft choices, reportedly will receive a No. 7 pick to go with Brown.

The source said Allen was making yet more trade overtures to another club when the Rams dismissed him. That club was not named.

A former associate of Allen's said the Brown trade was characteristic. "He overpaid for things he thought he had to have - with money that belonged to owners, or with draft choices from a club he might be leaving."

Don Klosterman, executive vice president and general manager of the Rams, reportedly was not in favor of the trade for Brown and told Rosenbloom that Allen had been hired as coach only and had promised not to interfere with the front office.

But Allen convinced Rosenbloom to make the transaction.

As the tension mounted at Los Angeles, conflicts reportedly developed between the assistants Allen brought in and the ones he retained from the staff of predecessor Chuck Knox.

Ram players accustomed to 3 1/2 hours of practice spread over two workouts a day under Knox complained about practices conducted by Allen - 2 1/2 hours in the morning and three more hours in the afternoon. "They were used to winning without that kind of work," Allin said. "They were spoiled."

Then came the boos at the preseason game in Los Angeles Saturday night against San Diego. The Rams lost, 17-0. Some of the fans were said to be sullen beforehand because of the projected move to Anaheim. Even the "Embraceable Ewes," the club's new cheerleaders, were booed because their introductions were lengthy.

The thinking is that the two straight exhibition losseswould not have been a factor - the Rams were 1-5 in the preseason in 1977 - but lumped together with the other problems, they served as a catalyst.

Allen said of his relationship with the front office: "I didn't think I had a problem, although there was still more friction left over from my years here before (under late owner Dan Reeves, who fired Allen twice before he made it permanent).

"I even scheduled a picture day when they wanted, even though they were taking pictures of guys I knew wouldn't be around later. I did everything I could to please them."

Allen conceded that he worked the Rams longer than his predecessor, but he remarked, "Still, you give a rookie head coach more than two games, don't you? And I'm not a rookie.

"I've always been a successful coach." Allen said. "This is a traumatic experience, but that's the way it is(in coaching) I'm shocked by the whole thing."