Of 12 Washington Redskins who became free agents yesterday and received qualifying offers from the team, tackle Mark May is the only one with an offer from the U.S. Football League, Redskins General Manager Bobby Beathard said.

May's base salary was $160,000 last season. The USFL's New Jersey Generals have offered him a three-year contract for approximately $400,000 a year, sources said.

The Redskins have offered him about $180,000 per year, those same sources said. That is believed to be the minimum they must offer to retain their rights to him. Beathard yesterday declined to discuss specifics of the Redskins' offer and said he doesn't know the details of the Generals' offer.

"We're in the process of trying to negotiate a contract with Mark," Beathard said. "My sources lead me to believe that they (the Generals) are in fact interested in him."

May, who is 6 feet 6 and weighs 295 pounds, was unavailable for comment. His attorney declined comment, as did Jim Valek, the Generals' general manager. Jay Seltzer, the team president, did not return phone calls.

Beathard and other sources yesterday called erroneous reports that May had imposed a 72-hour deadline on the Redskins.

May has played four years for the Redskins and is the team's only key offensive lineman who is not signed through at least the 1986 season. Among other starters, center Jeff Bostic will earn $215,000 in 1985, guard Russ Grimm $244,000, tackle Joe Jacoby $160,000 and guard Ken Huff $250,000. That includes base salary, reporting and roster bonuses, but not performance bonuses.

The USFL is not aggressively pursuing NFL free agents, but May is attractive to the Generals because they need to build an offensive line to block for Heisman trophy winners Herschel Walker and Doug Flutie.

May is one of 269 NFL players who formally became free agents yesterday. The Redskins said Thursday they had made qualifying offers to 12 of their 13 players who became free agents, including running back John Riggins, kicker Mark Moseley, defensive tackle Dave Butz and cornerback Vernon Dean.

The formality of making a qualifying offer to a free agent by Feb. 1 gives that team the right of first refusal to match any contract signed with another NFL team, or compensation if the team decides not to match the offer. Because of stiff compensation requirements, only one NFL free agent has signed with another league team in the last decade, according to the Associated Press.

Four first-team all-NFL selections are among the free agents: defensive tackle Randy White of Dallas, linebacker E.J. Junior of the St. Louis Cardinals and defensive backs Mark Haynes of the New York Giants and Deron Cherry of the Kansas City Chiefs.