Washington Redskins owner Jack Kent Cooke said today he believes unsigned running back John Riggins will reach an agreement on a contract and will arrive at training camp next Saturday as scheduled.

"Neither of us will have any difficulty, in my opinion, of meeting a resolution in this matter," Cooke said as he watched practice. "That resolution, I hope, will be successful for the club and for me . . . We're counting on John. We want John. I hope he will be here, and, more important, I rather think he will be here."

Cooke said he plans to meet with Riggins "soon" to discuss the Redskins' offer. In a television interview Thursday, Riggins joked that he could play "four or five games" on the basis of what the Redskins were offering.

"John is full of witticisms," Cooke said. "He's a humorous fellow. My experience with him is that you present him with a set of circumstances, a set of conditions, and he'll bend them to make a joke of them."

Cooke said he also expects to reach an agreement by Saturday with defensive tackle Dave Butz. "I cannot imagine otherwise," he said, adding that General Manager Bobby Beathard will call Butz, maybe on Sunday.

Cooke and Beathard would not comment on the terms of both contract negotiations.

As for kicker Mark Moseley, the other unsigned veteran, Cooke said, "That's entirely in Bobby Beathard's hands." Beathard would not comment, but indications are the Redskins expect him to be signed in time as well.

One other matter that remains unresolved is quarterback Joe Theismann's contract extension. A year ago, Theismann received a two-year extension of his contract, good through the 1987 season. But he has not signed the extension.

"We're still discussing it," Cooke said.

The status of the two draft choices missing from camp changed little today. During Cooke's two-hour meeting with Beathard and Coach Joe Gibbs in the team dormitory, the Redskins decided to ask Larry Muno, cornerback Tory Nixon's agent, and/or Nixon himself to come to camp to discuss his contract, Cooke said. Beathard said he had not spoken with Muno today.

Meanwhile, the agent for AWOL kick returner-wide receiver Jamie Harris arrived here today and met briefly with Beathard, who told him the Redskins have withdrawn their $335,000 contract offer and don't want Harris to return. "We will accept him back only at the lowest salary allowed by the collective bargaining agreement, with no signing bonus," Beathard said.

Agent Phil Tannenbaum said Harris was going to Houston tonight.

Free agent safety Kurt Kafentzis broke his left index finger in the morning practice and free agent offensive lineman Chris Osswald sprained his left ankle during a blocking drill.

Line of the day: Receivers coach Charley Taylor to rookie free agent wide receiver Boris Pendergrass, on a good catch: "Way to go, Teddy."