President Reagan sought to defuse a diplomatic dispute with Japan today by promising Prime Minister Zenko Suzuki a report early next week on the ramming of a Japanese freighter by a U.S. nuclear submarine.

The report on the April 9 incident, which took the lives of two seamen, will be handed to Suzuki Tuesday in New York, two days before he is to meet Reagan during a state visit to Washington, the U.S. Embassy here said.

Reliable sources said Reagan's promise was designed to take some domestic political pressure off Suzuki, who has been pressed hard at home to make an issue of the submarine incident when he meets the president.

Reagan earlier had said that "sufficient progress" would be made in resolving the dispute before Suzuki's visit, but that statement did not soothe the irritation of the Japanese press and some officials who suspected that the United States would try to cover up the reasons for the collision.

The immediate reaction to Reagan's latest message was favorable. One government official said it was "evidence that the U.S. is acting in good faith" and would probably help in easing the domestic political pressures.

The U.S. submarine George Washington rammed and sank a small Japanese freighter, the Nissho Maru, in international waters 110 miles southwest of Japan in a collision that is still being investigated.

The captain and crew member drowned, and 13 survivors drifted in the open sea for 19 hours before being rescued by a Japanese destroyer. The United States did not formally notify Japanese authorities in Tokyo until 35 hours after the collision.

Japan has insisted on knowing why the submarine did not rescue crewmen in lifeboats. The U.S. Navy has explained that the sub surfaced after the collision but saw neither a ship nor crew members in distress. There has been no explanation for the 35-hour delay in notifying Japanese authorities.

U.S. Navy investigators are still questioning the freighter's survivors in Japan and a final report may not be presented for several months.