The Washington Redskins, who probably will face a grievance hearing within two weeks over their decision to retire John Riggins, are also fearful that the veteran fullback will ask the National Football League Players Association for help in obtaining the first of his deferred contract payments. a

Riggins has not decided when he will ask the Redskins for the first deferred payment installment of $100,000. He says the club owes him a payment, under the terms of his contract, 30 days after he notifies them in writing of his retirement. He gave the team a written notice on July 31.

General Manager Bobby Beathard said yesterday the club had not decided whether it would pay Riggins now or refrain from starting the deferred money installments until after the 1981 option year of Riggins' contract has expired. But Washington apparently will fight any attempt by Riggins to have the payments begin immediately. Should that need arise, the Redskins fully expect Riggins to take the problem to the NFLPA.

"We haven't talked to John about the deferred money," Ed Garvey, executive director of the NFLPA, said yesterday. "But, yes, we could get involved in that issue if he asked."

The Redskins owe Riggins $800,000 in deferred money. It will be paid to him in eight $100,000 annual installments.

The deferment issue is just another facet of the increasingly bitter relationship between the Redskins and the veteran fullback, who now is ready to fight them on the retirement situation.

The NFLPA will file a formal request some time this week requesting a grievance hearing over the retirement issue.

"Once it is filed, we hope to get a hearing within a week or 10 days," Garvey said. The league's player-club relations committee, which comprises two players and two owners, will hear the complaint. If that group has a split vote, the issue will go to an arbitrator.

"Because this involves what we consider to be a suspension," Garvey said, "we feel the complaint should be considered as quickly as possible.John goes along with us on that. He gave his approval, although we would have filed a complaint anyway. It should be resolved in less than a month."

The NFLPA maintains that the league's "retired-left camp" list, the category in which Riggins is presently listed, is not valid. When a player is placed on that list, according to the league, he cannot play in the NFL the rest of that season.

Riggins says now that he doesn't want to be denied the option of playing this season, although he said he didn't have any objections when the club put him on the list Aug. 31.

"What if I wanted to come back in the middle of the season to help them out if someone was hurt?" Riggins said. "Besides, I don't think the 'left camp' list is right. And I asked to be retired, anyway. It was voluntary."

If Riggins and the NFLPA win, the Redskins would have to take him back, should he decide to play this year, trade him or waive him.

Beathard said that the club would pursue the retirement issue vigorously with the grievance committee. "I think that we are within our rights," he said. "But the players association wants to test the rule."

A check with other clubs in the league indicated that at least 12 other teams currently have players on the "retired-left camp" list. But Riggins is the biggest name by far.