The Japanese government, under pressure from opposition parties, officially asked the United States today to comment on reports that atomic warheads may have been stored on a U.S. ship anchored just off Japan's shoreline more than 20 years ago, a Foreign Ministry spokesman said.

It was the first official Japanese query about the reported presence of U.S. nuclear weapons since a political furor eruped two weeks ago.

Yesterday, Japan said today it has no records of its own to support, a former American ambassador's claim that the U.S. Navy routinely stored atomic bombs aboard a ship here, and called the story unfounded hearsay.

"We have no corresponding records. We believe that the U.S. government has been faithfully honoring its prior consultation commitments, and therefore we believe [the statement] is not possible," the Foreign Ministry said in its first official comment on the assertion by U. Alexis Johnson, who was ambassador to Japan in 1966-69.

Johnson's account was given to The Washington Post in answer to questions about a claim by a former Pentagon nuclear specialist, Daniel H. Ellsberg, that the U.S. Navy "permanently stationed" a ship carrying nuclear weapons 100 or 200 yards off the Japanese coast for a period that ended in 1961.

The account, which was given banner headlines here yesterday afternoon, may further complicate Japanese-U.S. relations, already buffeted in recent days by a series of defense-related controversies.

Last week, Japan's foreign minister, Masayoshi Ito, resigned after being accused of mishandling Prime Minister Zenko Suzuid's recent visit to Washington and not accurately reflecting the limits Japan put on its willingness to cooperate with the United States on military matters.

Vehement protests by Japanese commercial fishermen this week that U.S. and Japanese warships had caused $400,000 in damages to their nets during joint maneuvers in the Sea of Japan prompted the two countries to call off the exercise.

Thursday's accounts of storage of nuclear weapons just off the Japanese coast came only a week after another former U.S. ambassador, Edwin O. Reischauer, told reporters that nuclear-armed U.S. vessels have routinely been permitted to dock at Japanese ports, a claim that the Japanese government, extremely sensitive to charges of cooperation with a nuclear superpower, denied.

Johnson's account appeared certain to increase the public debate about the U.S.-Japanese military relationship that has given Suzuki his worst political crisis since taking office 10 months ago.

Suzuki asked the Foreign Ministry today to investigate Johnson's account, which, with Reischauer's claims, suggests tht U.S. warships carrying nuclear weapons are permitted to call at Japan's ports and pass through its waters despite a Japanese policy forbidding the production, possession or introduction of such weapons in Japan.

Suzuki again told parliament yesterday that a 1960 treaty forbids the introduction of nuclear weapons into Japan without prior consultation, and that Japan would refuse any U.S. request to carry nuclear arms into or through Japanese territory.

The U.S. position is that it respects Japan's restrictions on nuclear arms, but U.S. officials refuse to comment on the location or movement of nuclear arms anywhere in the world, including Japan.