Two hours after announcing the unexpected signing of rookie linebacker Larry Kubin, who had said he would play one more year at Penn State, the Redskins lost starting guard Fred Dean for at least four weeks with a ruptured muscle in his upper right arm.

Dean will undergo surgery on the arm Friday at Sibley Hospital in Washington. Coach Joe Gibbs said he could be out as long as eight weeks, depending on the extent of the tear, which occurred during practice Wednesday.

Dean had been starting ahead of veteran Ron Saul at left guard. Dean's place in practice today was taken by rookie Russ Grimm, the third-round pick from Pittsburgh, who also is a contendre for starting center. t

Kubin, a preseason all-America candidate last year who hurt his knee following the third game of the season, checked into camp and signed a series of three one-year contracts. Although he was chosen on the sixth round as a gamble by the Redskins, it is apparent he was given a higher-round contract to lure him away from Penn State. He had been granted a fifth year of eligibility in June because of the knee injury.

Kubin, who still is recovering from the ailment and cannot practice, was projected as a possible first-round pick next year. He said he finally decided to turn pro now "because I thought it would be too much of a financial risk to stay at Penn State. It was a better business decision to go pro now."