Call it a day of dismay for the Washington Redskins.

Certainly the most dismaying news of all today was the diagnosis that Mark May, starting offensive right guard, has suffered a partial tear of his right tricep muscle. May injured the muscle trying to hold off rookie Charles Mann in a pass-blocking drill Tuesday afternoon.

To fill May's void, the Redskins today moved durable Darryl Grant, the defensive tackle, back to right guard. Grant, a versatile 6-foot-1, 275-pound third-year player, began with the Redskins as an offensive lineman, before being converted to defense prior to last season.

Coach Joe Gibbs said he expects May will miss two weeks. Joe Bugel, offensive coordinator, said he is preparing Grant to start at right guard in the season-opener in five weeks against Dallas.

"We're getting Darryl ready for (Dallas defensive lineman) John Dutton," said Bugel. "Rather than going to the streets to pick up some guy off the waiver wire, we're picking one of the toughest guys around and he's right here."

May's injury might not have been so troublesome if Fred Dean, starting right guard in the Super Bowl, had not left for the U.S. Football League. Inexperience rests with Don Laster (second-year) and rookies Nate Newton and Bob Winckler, other possible right guards. And George Reihner, 26-year-old former Houston Oilers lineman the Redskins planned to coax out of retirement, failed his physical today because of a back injury.

In a sinister perspective, the Redskins now have lost Dean for good and May for an uncertain time, without replacing them with an experienced player. "If someone had told me that after the Super Bowl, I probably would have blown my head off with a shotgun," Bugel said.

"Darryl is a potential starter on both sides," Gibbs said. "Obviously, it's not easy. I could see Darryl starting, say, at right guard and if somebody got hurt, he could fill in on the defensive line, too . . . We're looking for somebody to really blossom."

Grant, who likely will be replaced at defensive right tackle by veteran Perry Brooks, said, "I've got a streak going: I've never played the same position for two straight years since I started in college . . . It's not an easy adjustment, but they need me, so I'm willing to try it."

Grant is the defensive tackle who caught Gary Hogeboom's deflected pass and ran 10 yards for a touchdown against Dallas in the conference title game last year. Bugel said if May isn't fully recovered when he returns, he will have to outplay Grant to return to the starting lineup.

Grant said with a smile, "No, this doesn't make me a Hog."

May said his right tricep has swelled a full 1 1/4 inches larger than his left tricep. He will not need surgery because his tear is not as severe as the ruptured tricep that caused Fred Dean to miss the entire 1981 season.

"I didn't get all the information about (the injury)," May said, "because once I heard there was a tear, I didn't feel like hearing anything else."

In another development, the agent for Jeris White, Redskins' unsigned 10-year cornerback, notified the Redskins today that he would like take White's case to arbitration.

Bobby Beathard, Redskins general manager, said he received the cable from Howard Slusher, White's Southern California-based agent, then sent a return cable back to Slusher late this afternoon, rejecting the offer.

"I told Howard that the Redskins have made their best offer already and we stand by it," said Beathard.

White, who does not speak to the press, has deferred all calls to Slusher. Slusher did not return repeated calls today.

White, 30, is seeking a three-year deal worth an estimated $1 million, including incentives and bonuses, it was learned. Last year, White had a $185,000 base salary last year, fourth highest on the team.

Arbitration is a negotiating process whereby a neutral arbitrator hears the facts and money figures presented by each side, then chooses one side or the other. There are no compromises.

Meanwhile, Redskins defensive end Dexter Manley, unhappy with his current contract, which expires .fter this season, met with owner Jack Kent Cooke and Beathard for 45 minutes today.

"It was just a meeting of two sides playing hard ball," said Manley, entering the final year of a three-year contract.

Manley, who led the Redskins with 9 1/2 quarterback sacks last season, is scheduled to make $60,000 this year, minimum for a third-year player. However, the Redskins have offered him a multiyear contract which includes $140,000 this season, a signing bonus and pay increments over the next several seasons.

"Mr. Cooke is a brilliant man and I'm a man standing up for what he believes is right," said Manley, 24.

Cooke did not comment on the talk, but Beathard said, "(Cooke) just wanted to get together to talk to Dexter. I've told Dexter all along that he's lucky he has an owner who stands behind him."

But the talk was not entirely cordial. Asked if the Redskins had threatened to trade him, Manley said, impishly, "Well, yes."

Asked if the rumors floating around camp--that the Redskins threatend him today with a trade to New Orleans, if his contract problems were not finished shortly--Manley's head snapped back. "I can't say," he said.

May was not alone on the Redskins' injury list: safety Greg Williams has a partial ligament tear in his left knee (out two weeks), defensive end Mat Mendenhall has a bruised right shoulder, wide receiver Mark McGrath has an intestinal stomach virus, offensive tackle Todd Hallstrom has a sprained toe and Rick Walker has a sprained toe and twisted knee.