The Carter administration has interrupted nuclear cooperation with Switzerland to retaliate against Swiss exports of technology to Pakistan that can be used to develop nuclear weapons.

This interruption in nuclear cooperation has been cloaked in diplomatic secrecy and comes only after a great deal of soul-searching by the Carter administration, which appeared a month ago to be ready to ignore its own nonproliferation criteria in order not to offend an important European nation.

After intense debate in Washington and sharp exchanges here in the Swiss capital, the White House and State Department have indefinitely delayed action on licenses the Swiss government badly wants so that it can have U.S.-supplied nuclear fuel reprocessed in France.

Switzerland wants to ship spent fuel from its four nuclear power plants to separate the byproduct plutonium. The plutonium, which also could be used in nuclear weapons, can then be reused.

The Carter administration also has blocked an unprecedented, undisclosed Swiss request for a license to sell to Italy plutonium that already has been culled from spent U.S.-supplied Swiss nuclear fuel in a French reprocessing plant.

U.S. officials have refused to discuss what eventually will happen to the Swiss nuclear transfer license requests, calling the dispute over the Swiss exports to Pakistan "an extremely sensitive matter."

It could become a crucial test of the Carter administration's publicly aggressive four-year campaign against nuclear proliferation. Especially in an election year, the ultimate White House decision on the Swiss license requests could have far-reaching ramifications.

A rejection could disrupt relations at a time when Switzerland continues to be a valuable link in communications between the United States and Iran on the American hostages held there.

Approving the Swiss license requests could risk another embarrassing conflict with Congress, which has been moving to overturn the Carter administration's decision to sell nuclear fuel to India.

Debate on a decisive vote on the sale to India is scheduled to begin in the Senate Tuesday. The U.S. Nuclear Nonproliferation Act of 1978, which is being used by Congress to try to stop the nuclear fuel sale to India, could also affect the White House decision on Switzerland.

Although U.S. officials concede that the Swiss government has impressively defended the technical international legality of the Swiss exports, some contend that Switzerland has violated the spirit of the 1963 Nuclear Nonproliferation Treaty. These officials require that the Swiss license requests be refused.

Switzerland needs the licenses to transfer the spent nuclear fuel and reprocessed plutonium because they are derived from fuel that Switzerland bought from the United States. Switzerland generates about 30 percent of its electricity with nuclear reactors and buys the vast majority of its nuclear fuel from the United States.

Under the nonproliferation treaty and U.S. law and agreements designed to prevent the spread of nuclear weapons, any nation buying U.S. nuclear fuel or technology must not transfer or sell it or any derivative to another country without U.S. permission.

The Carter administration has tried at home and internationally to discourage the development of reprocessing plants and fast-breeder reactors -- which while generating electricity "breed" more plutonium than they consume. The White House has argued that if plutonium proliferates, it will be easier to divert to, or be stolen by, nonnuclear nations or even terrorists for use in bombs.

The Carter administration, had approved previous Swiss requests for licenses to transfer used nuclear fuel to France and Britain for reprocessing. But the White House has been stalling for nearly two years on the Swiss request to sell plutonium to Italy because it has been unable to make a policy decision about whether it should allow any plutonium transfers at all.

Italy wants the plutonium for use in a giant French-Italian-West German fast-breeder reactor under construction in France.

The Carter administration more recently decided to hold up action on all the pending Swiss license requests because of new evidence that the Swiss government has allowed five Swiss firms to continue supplying Pakistan with technology that could produce nuclear material for bombs.

After Assistant Secretary of State Thomas Pickering formally complained about this a few weeks ago to the Swiss ambassador in Washington, the State Department informed the Swiss government that it was holding up action on licenses at least until Swiss officials satisfied the latest U.S. concerns about Swiss exports of nuclear technology to Pakistan.

In an interview here, Swiss nuclear policy official Claude Zangger said U.S. delegates to a Geneva conference of nations signing the nonproliferation treaty told him this month that the Swiss requests, "including the plutonium transfer, had finally arrived on President Carter's desk.

"But when I got back to Bern there was a Sept. 3 telex from Washington saying the procedure had been stopped by the State Department until questions were answered about the new information the U.S. had given us."

The U.S. Nonproliferation Act of 1978 states that U.S. nuclear exports and cooperation should be "terminated" to any nation found by the president" to have "assisted, encouraged or inducted any nonnuclear weapons state to engage in activities" involving nuclear materials that constitute "a direct, significant cause for the manufacture or acquisition of nuclear explosive devices and has failed to take steps, which, in the president's judgement, represent significant progress toward terminating such assistance . . ."

Swiss officials have been careful to make several distinctions concerning the exports of technology to Pakistan: the Swiss government has not recognized as a matter of policy that Pakistan is trying to develop nuclear weapons; it has no way of being certain if this is the purpose of Pakistan's purchases; the technology involved has a variety of applications besides the uranium enrichment process Pakistan is apparently developing to produce nuclear material for bombs, and none of the components appear on international lists of technology whose export is to be curtailed.

"The Swiss have been singularly unhelpful," said a Carter administration source. "The Swiss seem to be more legalistic than other governments, and this is a very tough problem to lick. Because the fact is the Swiss are legally correct. They are living up to their obligations."

U.S. suggestions that the Swiss government expand its narrow legal obligations to cover technology obviously destined for the Pakistani project that could produce nuclear weapons have been met by Swiss counteroffers to join international negotiations on expanding the international export control lists to include the components being exported by Switzerland. U.S. officials said the Swiss know this is impossible because of the components' multiple uses.

The United States, along with Canada, has adopted a system of requiring exporters to give the government "end-use" statements for items not on the international list to determine if they might be on their way to a bomb-building project. Swiss officials scoffed at this, contending that U.S. firms can and do lie in their end-use statements.

Switzerland drew sharp protests from the Carter administration once before, when it decided to sell Argentina a "heavy-water plant" that could produce weapons-grade plutonium even though Argentina has refused to sign the Nuclear Nonproliferation Treaty. The Carter administration earlier had persuaded Canada and West Germany not sell such a plant to Argentina unless it signed the treaty.

Some administration officials remain angry about that and are determined to punish Switzerland this time if legally possible.

Congress also could decide to step in under the 1978 law, as it has in moving to overrule Carter's decision to sell 38 tons of atomic fuel to India. m

Like Pakistan, India has refused to sign the nonproliferation treaty or to allow on-site inspections of all nuclear facilities to safeguard against the acquired nuclear fuel or technology being used to produce nuclear weapons. India exploded a nuclear device of its own in 1974.

Swiss nuclear expert Zangger said industrialists, energy officials and newspapers here have complained that what once seemed to be a secure supply of U.S. nuclear fuel and cooperation has now been made as risky by Carter administration nonproliferation policies as the supply of oil.

Before Carter became president, Zangger said, "approval of our requests took just a few weeks. Now it's months. We've had to tell Washington that we think anything more than six months would be excessive.

"Our nuclear trouble with the U.S. now means a loss of credibility with the man in the street for the U.S. and the nonproliferation treaty," he added. "People say we didn't have any trouble before we ratified the treaty in 1977, so maybe it was a mistake to ratify it."

Swiss Deputy Foreign Secretary Raymond Probst, formerly ambassador in Washington, said the question of whether the Carter administration will give Switzerland permission to sell plutonium to Italy "is not a Swiss problem. It is really a question of whether the U.S. is willing to allow the plutonium to be used in Super Phenix, the fast breeder being developed by the French-Italian West German consortium.

"We understand this is difficult when the policy of the Carter administration has been against fast breeders," Probst said.

"And there are other political elements involved, as shown by what happened to Carter's plans to sell uranium to India."

It could be argued that approving the transfer of the plutonium produced by reprocessing of spent nuclear fuel is only the next logical step beyond already frequent U.S. approval of transfers of spent nuclear fuel for reprocessing. Probst pointed out that the plutonium in question would never leave France, where it has been in a French reprocessing plant, and would merely be moved to the Super Phenix fast breeder.

Probst also suggested that an international study of the "nuclear fuel cycle" prompted by the president's efforts for stringent control of nuclear transfer might lead to "a rethinking" off the Carter administration's approach.

Some of Carter's policy has been seen as inflexible, unrealistic and unfair by some European countries more intent than the United States on developing nuclear power as a primary source of energy.

Despite the Carter administration's concerns about the production of too much plutonium usable for nuclear weapons, they are pushing ahead with sophiscated reprocessing and fastbreeder projects to guarantee a plentiful future supply of nuclear fuel.

Some British officials hope eventually it will be possible to develop a U.S.-British counterpart to Super Phenix. They are displeased that Britain, a pioneer in breeder technology and operator of a small, experimental breeder reactor, has now fallen behind, in part because of U.S. reluctance to agree to joint commercial ventures.

Some European officials believe they already see evidence of more flexibility in U.S. policy on reprocessing and fast breeders, and will be watching closely to see what decision is made on Switzerland's request for a license to sell plutonium to Italy for the Super Phenix fast breeder.