Japan's role as reluctant partner during the Iranian crisis has left new scars on its relations with the United States, but the experience has also jolted it into rethinking the way it plays its cards when economic interests are at stake.

Buffeted by criticism from without and within, government officials acknowledge Japan was slow to show support when U.S. hostages were seized in Tehran. They say they would act more quickly now. And some top leaders agree Japan must now start to look beyond its own economic interests in world affairs.

But the affair also has rekindled Japanese irritation at being publicly dragged along by U.S. pressures or being the butt of American complaints.

"We are always somehow in the dock," asserts Nobuhiko Ushiba, former trade negotiator and top-level adviser on foreign affairs. "We are always getting the complaints." Nevertheless, mirroring the country's divided state of mind, Ushiba agrees Japanm incorrectly mixed up its economic interest -- Iranian oil -- with a fundamental international rule of law by hanging back on the hostage issue.

Japan's first response to the hostage-taking was an innocuous statement of concern. Then Japan was accused of buying Iranian oil at high prices, undercutting the American boycott, and of dragging its heels on exerting financial pressures.

Concern about oil supplies was the reason. Japan gets 10 to 12 percent of its oil from Iran -- about the amount the United States received before it began its boycott of Iranian oil. When the storm broke, its trading companies were in Tehran negotiating a major new purchase for 1980.

Criticism of the oil-buying still rankles Japanese officials and some American diplomats agree it was unfair. Both sides say the United States never told Japan not to buy Iranian oil and that the government had acted to stop high-priced purchasing before accusations of oil profiteering were made by Secretary of State Cyrus Vance's press spokesman in Paris on Dec. 10. Charges of Japanese insensitivity were spread around the world, they say, even before Vance heard an explanation from Japanese Foreign Minister Saburo Okita.

U.S. Ambassador to Japan Mike Mansfield defends the Japanese version and in an interview last week spoke scornfully of the State Department's "diplomacy by press conference."

He said the embassy here knew nothing of American complaints or the plan to rake Japan in the press. "We were not kept clued in by the department," Mansfield said. "It caused some damage. We could have accomplished the same results in a quiet manner without causing troubles and criticism at home."

The ambassador also said Japan's Ministry of International Trade and Industry has responded quickly when it learned of the oil purchases and had forced the companies to sell at a loss.

Japan ultimately strongly criticized the hostage-seizure as a violation of international law and has been careful since to notify American officials of oil purchases from Iran. But there is still a feeling in official circles that the U.S. insistence on economic sanctions asks Japan to take an unfair risk of losing its oil lifeline, especially if the sanctions are first rejected by the United Nations Security Council.

"We want to help," said one offical, But if it is a matter of life, lots of Japanese would object and say, "were we consulted when the shah [of Iran] was allowed to come into the United States?""

The belief that Iranian oil is a "matter of life" for Japan is widespread and affects everything that is said or written about Japan's behavior. It is at the root of the government's ambiguity. At a news conference last week, Foreign Minister Okita was asked why his government could not speak our more clearly and forthrightly.

In a burst of candor, he replied: "If we say something clear-cut and straightforward, we might not be really serving the objective of Japanese diplomacy, which is to protect the Japanese people's lives."

Nevertheless, the criticism evoked by being ambiguous on Iran has left the Japanese in a state of what they like to call "self-reflection." Officials are sensitive to the complaint that Japan's foreign policy lacks principle and that it is always deliberately vague because vagueness serves Japan's self-interest.

Okita also indicated a measure of soul-searching. For three decades, while it was rebuilding its economy, he said last week, Japan was little concerned with international affairs that did not involve its own interests. That cannot continue, he added, even though it will require a change in the Japanese mentality. Ushiba, who has negotiated in major economic feuds with United States, shares that view. The fact that Japan had to switch tactics quickly on the Iran-hostage issue, he said in an interview, was "a great shame on the part of the Japanese foreign policy" because it gave the appearance once again of bowing to American pressures.

Japan should never have mixed up her oil interests with principles of international law, he said. It must realize it is living under "fundamental international rules" even if circumstances "interfere with our economic interests," he said.

There have been hints of substantive changes, too. Japan delivered a prompt and clear-cut condemnation of the Soviet invasion of Afghanistan, although it is fearful of alienating its big Communist neighbor as it is of losing Iran's oil. It is planning several modest measures to register displeasure with the Soviets, although it will not take part in sanctions.