Pyatras P. Grishkyavichus, 63, longtime Communist Party chief in the Soviet Baltic republic of Lithuania. Grishkyavichus had been first secretary of the Lithuanian party since 1974. He was also a member of the party's policy-making Central Committee and a deputy in the Supreme Soviet, the nation's nominal parliament. After the 1941 German invasion, Grishkyavichus, a member of the Komsomol Communist Youth League, fled eastward with the Red Army. He fought with the Soviet forces in 1942 and in 1943 was parachuted into German-occupied Lithuania, where he joined up with a partisan unit. Grishkyavichus joined the Communist Party in 1945 after the Soviets had driven the Germans from Lithuania. In Moscow on Saturday of unannounced causes.