The European allies are balking at joining the United States in imposing economic sanctions against Iran, but they have indicated they do not intend to take advantage by moving in to pick up trade American businesses are forced to drop.

With the exception of Britain, which may follow the United States with some symbolic unilateral actions of its own, the allies plan to limit their support to public statements and promises not to undercut Washington's moves.

This, West German officials said, is what Chancellor Helmut Schmidt meant yesterday when he told the Bonn parliament that "if the United States finds it necessary" to announce economic sanctions, "it can rely the support of West Germany as an absolutely trustworthy ally and friend."

Nevertheless, Britain, West Germay, France and Italy -- Iran's prinicpal trading partners and bankers in Europe -- have scrapped the plans they made to obey the proposed sanctions order that was veoted by the Soviet Union in the U.N. Security Council last Sunday.

In Tokyo, meanwhile, a special assistant to the U.S. Secretary of State, Philip Habib, reported yesterday that the Japanese government had pledged to "do its utmost" to support U.S. opposition to both the Soviet intervention in Afghanistan and the holding of American hostages in Iran, news agencies reported.

[However, neither Japanese nor Americans officials would say exactly what Japan was prepared to do in that regard. Habib noted that "major political decisions" would have to wait until after the return of Prime Minister Masayoshi Ohira and Foreign Minister Saburo Okita from a state visit to Australia and New Zealand.]

The Europeans believe sanctions against Iran would endanger their own economies and go against Western Foreign policy interests. Thus, they have reached virtually the same position on U.S. sanctions against Iran as they have on American retaliation against Moscow for the Soviet Union's invasion of Afghanistan: The allies will not join in drastic actions that they feel will threaten the dialogues between the East and West and between the developed nations and the Third World.

Furthermore, European officials say, without the legal obligation a U.N. order would provide, they should not end the remaining trade they have with Iran, further interfere with their bankers' business with the Iranians, nor risk cutting off their supplies of Iranian oil.

The allies also believe, according to diplomats, that harsh economic sanctions would further alienate the Iranian people at a time when the West should be using the threat of the Soviet invasion of Afghanistan to Iran and other nonaligned countries to woo them closer to the Western camp. Furthermore, some allies, especially West Germany, fear that enforcement of economic sanctions against Iran by blockading or mining the Persian Gulf could lead to a dangerous military confrontation with the Soviets.

After consultations with U.S. Deputy Secretary of State Warren Christopher earlier this week in London, Rome, Paris and Bonn, European officials say they believe they have reached an understanding by which the Carter administration will move cautiously to impose economic sanctions by itself to pressure Iran to free the American hostages held at the U.S. Embassy in Tehran.

In Bonn, West German officials said Schmidt did not detail any actions his government would take to join in U.S. economic sanctions because there would not be any. Schmidt also was careful to avoid promising support for any U.S military moves to try to force Iran to free the hostages.

"Schmidt cannot say it aloud, but he fears that the Americans, in the matter of sanctions, will start something he can't stop," the influential West German daily, Sueddeutsche Zeitung, pointed out today. "His misgivings are reflected less in what he says than in how he says it and what he does not say."

France staunchly opposes all economic sanctions or other actions that could interfere with its own trade and diplomatic objectives, Ital, whose diplomats argue against sanctions on philospohical grounds, could lose about 13 percent of its total oil supply if the Iranians carried out their threat of cutting off oil to any country imposing sanctions.

Even Britain is reconsidering its position, despite Prime Minister Margaret Thatcher's strong public promises of support for President Carter in the Iranian crisis. British officials share the other allies' skepticism about the legality of imposing trade and banking sactions without a U.N. order and are concerned about the potentially harmful side efforts of economic crubs.

"Thatcher still wants to try to help Carter and honor her pledge to him," one source said. Exactly what the British may do, however, will not be determined until after Carter acts.

British officials said they now expect Carter to continue "a step-by-step, gradual tightening" of the pressure on Iran. The allies were dismayed when American officials said immediately after the Soviet veto of the U.N. sanctions that the United States was going to impose the across-the-board sanctions anyway "without delay" and that is expected the allies to do the same.

European officials let it be known that they were displeased to have this kind of indirect pressure put on them before their governments had a chance to consider the next steps. They told Christopher they doubted that they could join U.S. sanctions without U.N. approval, but they would give the United States moral support if it felt it had to go ahead alone and did not do anything rash.

West German and British officials also have stressed their countries' commitment to allied unity, loyality to the United States and understanding of the U.S. dilemma over the plight of the American hostages in Tehran.

Yet the allies remain in philosophical disagreement with Washington over the wisdom of tough economic sanctions. Senior European diplomats believe such sanctions are unlikely to persuade the hostages' apparently "irrational" captors to free them and may only make more difficult ongoing, behind-the-scenes diplomatic negotiations with the increasingly nervous government of Alyatollah Ruhollah Khomeini.

British officials believe it would be unwise for the United States to act before Iranian national elections, set for Jan. 25, because no change in the hostage situation could be expected before then anyway, or the summit of Islamic nations meeting the next day in Pakistan to discuss the Soviet invasion of Afghanistan.

European diplomats suggest that informal cooperation between the West and Islamic nations to counter a Soviet threat to the Middle East and South Asia might include attempts to convince the Iranians that they should free the hostages and move closer to the West for their own protection.

"We see these two things are linked," a senior Italian officials said, "but not necessarily in the same way the Americans are linking them, as reasons to take drastic actions. Carter's moves are seen by some as overreactions that could backfire in the long run."

The Europeans reaction to the Iranian crisis parallels their approach to the events in Afghanistan. Consequently, West German, Italian and French trade in advanced technology to the Soviet Union for Soviet oil, gas and uranium is matched by their trade with Iran in return for Iranian oil, although the volume of the latter has been cut sharply by the turmoil of the Iranian revolution.

"I'd say [Kohomeini] has already ddone a pretty good job of embargoing British trade, most of which has been brought to a fairly abrupt halt," said an economic analyst for the Association of British Chambers of Commerce, European embassies long ago warned their nationals to leave Iran and few new contracts offered by the Iranians -- no matter how lucrative -- have been taken up by Europeans.

But a portion of the commerce continues, hundred of Europeans still live in Iran and British and West German banks still hold large Iranian deposits and loans. Although Britain does not need Iranian oil, British Petroleum, partly owned by the British government, and Royal Dutch Shell of Britain and the Netherlands, buy and refine Iranian oil for sale to the other European countries.

Just recently, BP and Shell signed new contracts to renew their supply of crude oil from Iran. The two multinational oil companies also agreed, with final details now being worked out, to refine and help market some of the Iranian oil on behalf of the state-owned National Iranian Oil Co., which would make BP and Shell virtual partners with the Iranian government in these deals.

European businessmen and bankers are strongly opposed to having their financial relations with Iran further disrupted by economic sanctions. The bankers also fear that any government interference will scare away other oil-rich Middle East countries that now are among their most important customers.