KARACHI, Pakistan, Aug. 21 — The Pakistani radio reported today that Pakistani troops attacked a hideout of Indian agents in the Sundarbans forest area in East Pakistan yesterday, killing 51 and capturing 9.

The radio said the hideout had been found at Syamnaagar, five miles from the Indian border. The troops made a surprise attack, according to the radio, causing those in the hideout to run in panic toward the border.

Those taken prisoner were reported to have said that the camp had been commanded by a captain from the East Pakistan Rifles, a paramilitary organization that had rebelled during the military action against secessionist elements in East Pakistan last March.