TOKYO, JAN. 31 -- Suppose the Japanese Diet, bowing to widespread public opposition to the Persian Gulf War, refuses to approve the $9 billion contribution that Prime Minister Toshiki Kaifu has pledged for the U.S.-led multinational force.

That scenario was raised this week in a report by the research department of Salomon Brothers Inc.'s Tokyo office, which warned of dire consequences for Japanese financial markets if opposition parties force the Kaifu government to weaken its support for the anti-Iraq effort.

As Japan's Diet, or parliament, became embroiled in a debate over the aid, the Salomon analysts wrote that "confidence in the yen and Japanese assets" are at stake and the markets will be heavily influenced by "the willingness of the Japanese people to accept the {ruling} Liberal Democratic Party's goal of a broader international role for Japan."

The Salomon scenario probably won't come to pass; political insiders expect Kaifu's $9 billion plan to win Diet approval, albeit narrowly.

But the investment firm's report reflects the growing consensus that as far as Japan's economy is concerned, the biggest damage from the gulf war is unlikely to come from high oil prices or shaken consumer buying sentiment. The more significant danger lies in the potential for a severe international reaction to any perceived failure by Japan to shoulder its fair share of the war burden.

"Among the most important issues that the gulf crisis raises from the perspective of Japan's position in the world economy is the question of the country's ability, indeed its willingness, to assume positive international responsibilities," Kenneth Courtis, senior economist for Deutsche Bank Group in Tokyo, wrote in his weekly report to clients.

The gulf war's direct effect on Japan's economy appears to be minimal, Courtis said. "Oil is cheaper today, in yen terms, than it was before the invasion of Kuwait," he noted. Japan has built up four months' supply of petroleum, and it has become highly energy-efficient, producing about 2.4 times the output with the same energy as it did 15 years ago.

Courtis contended, however, that Japan "has aimlessly squandered enormous amounts of political capital" because of its hesitant, often fumbling response to requests for active support from the United States and other nations involved in the fight against Iraq.

This "vacuum of leadership" and the anger in Washington and other capitals "sets Japan up for much more intense international pressure to open its markets. ... It also means that Japan's economic activity abroad will come under still more intense scrutiny."

Already, critics have sought to use the issue of Japan's gulf contribution to prod Tokyo into making trade concessions. Chrysler Corp. Chairman Lee Iacocca, for example, asserted that Japan ought to restrict auto exports because Americans would soon be making sacrifices "in an area of the world that supplies most of Japan's oil."

For now, the sum offered by Kaifu has drawn expressions of appreciation from members of Congress, and virtually no one is calling on Tokyo to send troops to the gulf, which would violate its postwar peace constitution.

The $9 billion, which comes on top of $4 billion previously committed, is equivalent to about $76 for each Japanese. To cover these pledges, the government today proposed doubling oil taxes, increasing the cigarette tax 7 1/2 cents a pack and raising corporate tax rates.

But the package has become snagged over protests that the money must not be used to buy weapons and ammunition, and Kaifu's party is trying to reach a compromise on the issue in the upper house of the Diet, where it lacks a majority.

The aid issue became a political minefield here after Secretary of State James A. Baker III said last weekend in Washington that the Japanese money would all be used to pay for U.S. military expenses.

Ever since the remark -- quickly labeled here the "Baker hatsugen," a Japanese word that is often used to mean "gaffe" -- Kaifu has been on the defensive. The Baker "gaffe" has become a central topic of the sometimes angry gulf debate underway in the Diet.

Many Japanese feel the country's pacifist constitution -- imposed on Japan by the U.S. occupation in 1947 -- makes it illegal to fund a war effort, even when Japan isn't fighting. Accordingly, Kaifu is promising that none of Japan's $9 billion will go "directly" to military uses. Instead, it will be used for logistics, food, and similar troop support needs, he says.

Japan's third-biggest political party, the Komeito, says it will support the $9 billion donation only for nonmilitary purposes. If Baker's remark were taken at face value, Komeito might vote against the contribution and it probably couldn't pass the Diet.

Japan's government also has contended its gulf aid is going to the multilateral force -- not just to the United States.

This is an important distinction politically because Kaifu is under fire for being excessively beholden to the United States. The Japanese government was so determined to avoid the suggestion that it is playing the role of Bush's banker that it set up a complicated round-about route for its aid to the gulf effort, including $2 billion already disbursed.

The money first goes to the Gulf Cooperation Council, an organization of six allied Middle Eastern countries, and is deposited in an account called the "Gulf Peace Fund." The gulf council is then supposed to disburse money from this fund.

In practice, the money goes mainly to the U.S. military. However, Kaifu can assert, with literal accuracy, that Japan is not paying the United States for the war but is contributing to a multilateral fund.

That kind of arrangement, known here as tatemae -- the Japanese word for facade -- is a common face-saving gesture in Japanese society. Baker's statement punctured the facade, causing Kaifu serious political problems.

Even if, as expected, the $9 billion is eventually appropriated, more trouble could be lurking down the road. Extracting more money from Tokyo for a prolonged war could prove difficult. Local elections are scheduled for April, and the opposition Socialists are planning to make the war a major issue.

All this comes against the backdrop of an economy that otherwise is so robust that the Bank of Japan, which has been hoping for a slowdown to help contain inflation, plans to keep interest rates high until more clear signs emerge of a cooling trend. "This is no time to change our policy stance," a senior central bank official told reporters today.

But what would happen to financial markets, he was asked, if the Diet rejected the Kaifu plan on the gulf war?

"I don't even want to think of the situation," he replied.