Chuck Knox, whose teams gained the National Football Conference playoffs five straight years but never reached the Super Bowl, quit the Los Angeles Rams yesterday to become head coach of the Buffalo Bills.

At the same time, the Detroit Lions hired former San Francisco 49ers coach Monte Clark to be their new head coach and director of football operations.

The Rams' search for a successor to Knox started even before it was officially announced the Knox would accept Buffalo's offer of a six-year contract worth $200,000 annually.

Don Coryell, coach of the St. Louis Cardinals, talked with the Rams Tuesday and the Cardinals let it be known yesterday they would let Coryell out of his contract, which runs through 1980, in exchange for a first-round draft choice.

Other possible candidates for the Rams job, according to wire service reports and NFL sources, are George Allen of the Redskins, Bill Walsh of Stanford and Ted Marchibroda of the Baltimore Colts.

Ram owner Carroll Rosenbloom said he will take from 10 days to two weeks to make his selection.

Knox and the Rams just last week signed a five-year contract, which at the end of each season would have automatically had another year added to its duration, at $150,000 per season.

"I think Chuck thought I didn't want him to stay and that was pretty true," said Rosenbloom. "The top line is to win, but fans in Los Angeles not only want to win, but to have a team that is exciting while doing it.

"We have always seemed to lose the big ones," Rosenbloom continued, "Chuck didn't let go on the attack."

"Chuck Knox was not let go," Rosenbloom added. "We met last week and came to an understanding. It was decided then that we would take a week to think things over, during which time he was given permission to talk to other clubs and we gave him to understand we would talk to other coaches."

Rosenbloom said he believes Knox was disappointed a year ago when he didn't get the chance to go to Detroit, where he had been under consideration as coach and general manager.

"We asked for compensation and they didn't come up with anything," the Rams owner said. Knox had complained that he hadn't been given the opportunity to talk officially with the Lions.

This time Knox was given permission to talk with any team where he thought he could improve himself.

"It came down to a simple fact that it was a unique opportunity and challenge for me and my family and I decided to take the challenge," said Knox, whose record in Los Angeles was 54-15-1. He replaces Jim Ringo at Buffalo.

Clark, meanwhile, has a five-year mandate to restore the Lions to respectability.

"He will report directly to me," said Lions owner William Clay Ford. "He is head coach and director of football operations, which is a brand new position and title for the Detroit Lions.

"He expressed a desire that he wanted control over his destiny," said Ford, who, on paper, is giving Clark something he has not granted any of the four men who preceded the former defensive and offensive lineman as Detroit's coach.

"He has given me the authority to effect my own personal approach to the job," said Clark, who will be 41 on Jan. 24. "I intend to rely heavily in the future on the draft."

"His job will include the college draft, scouting, waivers and trades," Ford said. "Final approval of trades, however, will rest with me."

Clark coached the 49ers to an 8-6 season in 1976 after a six-year apprenticeship under Don Shula in Miami. But a change in ownership lead to his ouster between seasons. Tuesday, 49er president Joe Thomas fired Ken Meyer and replaced him with Pete McCulley.

The candidate most likely to replace Knox appeared to be the disgruntled Coryell.

But Rosenbloom pointed out that Coryell, whose Cardinals had a disappointing 7-7 record last season is tied to a contract with St. Louis that runs through 1980.

"If Don Coryell were free, which he is not, we would proabably be interested in talking to him again," said Rosenbloom.

However, Cardinals owner Bill Bidwill said today he put Coryell in touch with the Rams.

Bidwell said he talked to the Rams after Coryell criticized the Cardinals' policies on drafting players and spending money.

Bidwell said after Coryell's "public statement following the loss to the Redskins (Dec. 10) we had a major problem. Realizing Don was unhappy in St. Louis and knowing his desire to take his family to a warmer climate, I contacted Los Angeles Rams general manager Don Klosterman.