Washington Redskin fullback John Riggins, who sat out last season in a contract dispute, is expected to return to Redskin Park today for a three-day minicamp, his first appearance as a Redskin since he left training camp last July. He also plans to report to training camp next month.

Ed Garvey, executive director of the National Football League Players Association, who is supporting Riggins in his dispute with the Redskins, said Riggins plans to attend the minicamp, which comes the week before his dispute with the team is set for arbitration.

"He's a player. He'll be there," said Garvey, who also said that Riggins plans to attend the Redskin training camp next month in Carlisle, Pa.

In another contract dispute, Bobby Beathard, Redskin general manager, said that offensive tackle Mark May, the Redskins' first-round draft choice, has not yet signed with the team and will not attend the minicamp. "The problem is figures. We're way far apart," Beathard said.

Riggins, who was the team's leading rusher in 1979 with 1,153 yards gained, was not available for comment, but his wife, Mary Lou, said in Lawrence, Kan., that he plans to attend the minicamp. Since midwinter, Riggins has denied interview requests.

Beathard said he has heard periodic rumors of Riggins' return since the fullback left. "If he shows up, that will be fine. If he doesn't, we won't be surprised," Beathard said.

Garvey said it was his advice that Riggins attend the minicamp.

"He received a letter from (Redskin Coach) Joe Gibbs inviting him to the minicamp, and he asked me what he should do. I told him to go to the minicamp.

"The Redskins made it impossible for him to play football last year. This is his first chance to play football this year," Garvey said.

He said he did not think Riggins' appearance at the minicamp would have any bearing on the arbitration but that "maybe the fans will know he wants to play football."

Riggins, who left training camp last summer after the Redskins failed to meet his demand that the option year of his contract be changed to a one-year, $500,000 guaranteed contract, was subsequently placed in the "left camp-retired" category, making him ineligible for play with any other National Football League team last season.

Riggins and the players association filed a grievance charging the Redskins had effectively denied Riggins the right to pursue his livelihood.

The grievance was heard by a committee of league and players association representatives, but the panel deadlocked, 2-2, sending the issue into binding arbitration. During those hearings, Riggins said for the first time that he wanted to resume playing last season.

Bert Luskin, a professional arbitrator from Chicago, is scheduled to hear the case in sessions scheduled here on Tuesday and Friday of next week. A decision could be as far off as the opening of training camp next month, although Garvey said Riggins plans to report to Carlisle even if the arbitrator has not ruled by the opening of camp.

At issue in the hearings are expected to be questions concerning the legality of the left camp-retired category, whether it was properly applied in Riggins' case and the matter of Riggins' compensation for last year.

Should Riggins lose the arbitration, he would have one year left on his contract -- at $300,000 a year -- plus the option year, the same situation that existed when he left camp last July.

A finding in Riggins' favor could bring him the $300,000 in lost compensation for sitting out last season and a ruling that he is now entering the option year of his contract.

Earlier in the winter, the Redskins actively had been trying to trade Riggins, but Riggins had refused to talk to representatives of any other clubs when they called his house. Under terms of his contract, Riggins had the power to veto any trades.

Then, in March, Gibbs stopped at Riggins' home in Lawrence, Kan., en route back from league meetings in Hawaii. Gibbs said at the time that they discussed Redskin plans and how much Riggins meant to the team, but that Riggins was noncommital about returning. He did say that if he returned to football, he wanted to play for the Redskins and not another club, according to sources.

On the matter of May, a 6-foot-6, 265-pound Outland Trophy winner from the University of Pittsburgh, Beathard said he has every hope of reaching an agreement, but he acknowledged there is a wide gap between the two parties. He has had similar disagreements with other draft picks that have been resolved successfully, Beathard said.

Beathard also said defensive end Karl Lorch is vacationing in Hawaii and has been excused from the minicamp. Another defensive end, Coy Bacon, has not yet signed and will probably not be at the minicamp, Beathard said.