Washington Redskins offensive tackle Mark May is considering a $400,000-a-year contract offer by the New Jersey Generals of the United States Football League, it was learned last night.

Unconfirmed reports had May, newly a free agent, giving the Redskins 72 hours to match the offer.

Sources said the Redskins had offered May a $180,000 salary. General Manager Bobby Beathard said he talked to May and his agent yesterday about negotiating.

Beathard said he knew of the Generals' contract offer but didn't know the figures. He denied May had given him an ultimatum. May could not be reached for comment.

May is one of 13 Redskins -- including running back John Riggins, kicker Mark Moseley and three other starters on the NFC Eastern Division champions -- who became free agents today. Under National Football League procedures, the Redskins have made qualifying offers to all of them except reserve linebacker Trey Junkin.

In addition, the Redskins have exercised the option year on the contracts of four other players.

By making the qualifying offers and by exercising the option year by Feb. 1, the Redskins formally retain right of first refusal for the players. "We're just protecting the team's interests," Beathard said.

Although Beathard said he expects to sign all of the free agents, he remains uncertain whether Riggins will play at age 36 and with back problems. "I don't know what John's status is, and I don't think John knows what his status is," he said.

Other Redskins who became free agents today are defensive tackle Dave Butz, cornerback Vernon Dean, defensive lineman Tom Beasley, linebacker Pete Cronan, wide receiver Alvin Garrett, quarterback Babe Laufenberg, wide receiver Rich Mauti, wide receiver Mark McGrath and cornerback Ricky Smith.

The four whose option years were exercised are free safety Curtis Jordan, tight end Rick Walker, offensive lineman Rick Donnalley and offensive tackle Morris Towns. Under NFL procedures, these players will receive a 10 percent pay raise should they not settle on a new contract.

If any of the free agents arranges to sign with another team, the Redskins can match that club's offer and keep the player.

If the Redskins decide not to match the offer, then they would receive compensation based on the player's salary. But there has been little movement in the NFL free-agent market, because of the required compensation, basically in high draft choices.

After Jeff Bostic was injured, Junkin was the team's deep snapper. But the Redskins expect Bostic to be recovered from knee surgery, and Darryl Grant can snap if needed.

Junkin is expected to sign with an undisclosed USFL team, according to Beathard and Charles Casserly, assistant general manager.

At least five other Redskins are going into their final contract year. One is Art Monk, who set a league record with 106 pass receptions in the 1984 regular season.

Beathard and Monk's attorney Richard Bennett said they are close to agreeing on a new contract for the wide receiver.