In a move reflecting a wary wait-and-see attitude toward the developments in Poland, the Soviet leadership has selected a relatively junior member as its representative at the Polish Communist Party congress.

The choice of Politburo member Viktor Grishin was interpreted by diplomats as Moscow's way to signal a cautiously noncommittal attitude toward a Communist Party congress whose outcome in uncertain.

By sending a man who is not known to be a member of the inner circle around President Leonid Brezhnev, the Soviets appartently sought to avoid the risk of embarrassment should the Polish meeting take what Moscow would regard as an exceptionally undesirable course.

More important, according to East European sources, the selection dissociated all key Kremlin figures from the outcome of the congress.

But Grishin, 66, is a respectable figure with experience in the Soviet trade union movement. He is chief of the Moscow Communist Party organization and was once head of the Soviet trade unions and associated with an abortive reform attempt to bring workers into management.

At the previous Polish party congress in February, the Soviet delegation was led by one of the senior Politburo figures, Mikhail Suslov.

Suslov visited Warsaw three months ago for talks with the entire Polish communist leadership. The talks ended in an open discord and were followed by a series of Soviet warnings that the Polish party's existence was endangered. a

Since the visit to Warsaw by Politburo member and Foreign Minister Andrei Gromyko 10 days ago, Soviet criticism of the Polish developments has become restrained.

The Soviet media has virtually ignored preperations for the Polish party congress with the exception of occasional commentaries on Moscow radio and television. Tonight, Moscow radio again assailed "right wing revisionist forces" in the Polish party, but expressed the hope that the "Marxist-Leninist forces" would prevail at the congress.

Despite uneasiness here, it is impossible to assess future Soviet moves should the congress take an unusually reformist course.