Jim Plunkett, at 40 the National Football League's oldest player and the MVP in the 1981 Super Bowl, was released by the Los Angeles Raiders Monday, apparently ending a 17-year professional football career.

While Plunkett was leaving the Raiders' camp in Oxnard, Calif., another veteran was going in the opposite direction as 34-year-old Joe Fields, released by the New York Jets last winter, signed with the New York Giants as a backup center.Monday was a big day for cuts as teams continued the process of whittling down their rosters although rosters do not have to be reduced to 60 players until next Tuesday.

Among other name players released were quarterback Robbie Bosco, the former Brigham Young star, cut by Green Bay, and safety Tony Lilly, who started for Denver in last January's Super Bowl.

Bosco, a third-round draft choice in 1986, spent his first two years on injured reserve, then competed 2 of 4 passes Saturday night in an exhibition against Indianapolis. His departure left ex-Raider Marc Wilson, Randy Wright, Don Majkowski and Blair Kiel vying for quarterback jobs with Green Bay.

In addition to Lilly, the Broncos also cut two other veterans: nose tackle Tony Colorito and fullback-tight end Bobby Micho.

Plunkett, the 1971 Heisman trophy winner at Stanford, was the first pick in the NFL draft that year by the New England Patriots. He played for New England and San Francisco before joining the Raiders in 1978. Plunkett led the Raiders to Super Bowl victories after the 1980 and 1983 seasons.

The San Francisco 49ers added three veterans to their roster as holdout cornerbacks Tim McKyer and Don Griffin signed one-year contracts and offensive tackle Bubba Paris returned from a 13-day visit to a diet center.

McKyer and Griffin showed up in the afternoon with agent Steve Weinberg and signed contracts believed to be for $300,000 each, plus incentives. The two players, both starters, wanted their original 1988 contract terms be improved.