The U.S. government quietly approved the export of 1.000 pounds of enriched uranium to three European nations only 24 hours before a congressionally imposed ban on nuclear fuel exports to Common Market countrys went into effect.

In an apparent attempt to avoid an immediate new confrontation with Western Europe over nuclear policies, the Nuclear Regulatory Commission (NRC) sped through 10 export licenses for shipments to France, West Germany and Denmark on April 7, one day before the recently enacted Nuclear Non-Proliferation Act of 1978 required that such shipments be halted.

The Common Market countries are pushing ahead with a plutonium-based breeder reactor nuclear energy program of the sort that the Carter administration has sought to delay in the United States. The Europeans depend on the United States for over 10 percent of their enriched uranium shipments. These shipments are available from no other source, and if the United State cut them off it would be a major blow to European energy development.

Many of the licenses had been pending for a year. Administration spokesmen asserted that President Carter had sent his personal approval on nine of the licenses to the NRC for final action months before the April 7 flurry of activity. The spokesmen could not immediately provide the dates of the presidential approvals.

Carter's ambitious efforts to curb nuclear proliferation have created serious strains with American's West European allies over the past year.

Now, however, his administration appears to be trying to find a way out of an impasses created by strict new limitations Congress is seeking to impose on the nuclear program s of other nations and by hostile West European reaction to the congressional demands.

Although lessened by the NRC's last-minute actions, the possibility of confrontation lingers. All shipments of U.S. enriched fuel to Common Market countries are now frozen. At least 22 export applications further back in the pipeline did not meet the April 8 cutoff, according to U.S. and European sources, and they now languish in a legal limbo that the administration and the European Commission, the Common Market's executive arm, are seeking to resolve.

These applications for export licenses involve the shipments of at least 1,000 pounds of enriched uranium to Italy, West Germany, Franch, the Netherlands, Belgium and Great Britain.

The Non-Proliferation Act. called the Glenn-Percy Bill after the two senators who sponsored it, became law five weeks ago. It required the Common Market's nine member countries to renegotiate the existing European-U.S. nuclear fuel supply agreement and in effect to accept an American veto right over the reprocessing of spent fuel.

Reprocessing techiques that separate plutonium from used fuel can be used to manufacture atomic weapons.

Led by France's President Valery Giscard d'Estaing, the Common Market's heads of state pointedly let the American-imposed April 8 deadline ship past without responding to Washington. Meeting in Copenhagen on April 8, the heads of state declined to put any mention of the issue in their final communique.

Two days before the summit the European Commission's top energy expert, Guido Brunner. publicly called on the heads of state to "limit the damage" to European-American relations by expressing "a readiness to talk to the Americans" on renegotiating the fuel supply agreement.

This appeal paralleled private suggestions from the State Department that any European response expressing a willingness to talk could enable Washington to continue shipments, according to informed sources.

But the Europeans refused to budge. Even Brunner's unsuccessful call for a compromise underscored the deep irritation that European leaders feel over the Non-Proliferation Act. Brunner said that "waving an embargo of uranium supplies in the face of close allies" was "not very smart."

France is likely to ensure that discussions on a Common Market reply drag out for several months, French sources in Paris report, adding that the eventual EEC response will probably be nothing more than a mild expressible renegotiations, at some future time. It will then be up to Carter to decide if such a statement would be grounds for ending the freeze on fuel shipments.

Traditional French political sensitivity about being seen to be dominated by American actions accounts in part, for French leadership on this issue. But there are also more pragmatic considerations. France is staking its economic future on replacing oil-generated energy with nuclear power, and is extremely sensitive to any threat to enriched fuel supplies and to its fast breeder program.

While willing to accept the principle of renegotiation. West Germany backs the French view that the current Euratom fuel supply agreement, which runs until 1995, cannot be canceled by an act of Congress.

France also argues that the Carter administration has committed itself in the two-year International Fuel Cycle Evaluation Program and through its actions in the London Suppliers Group not to disturb unilaterally the current flow of fuel.

One export license held up indefinitely in Washington is a shipment of 120,000 pounds of uranium to West Germany, where uranium was to be fashioned into fuel rods for re-shipment back to the United States. The final destination of the uranium is American electric power plants.

Nine of the 10 export liceses approved the night of April 7 by the Nuclear Regulatory Commission had been previously approved personally by President Carter under his own instructions to the State Department and the NRC.

Carter examines all requests for shipments of more than 30 pounds of high enriched uranium, or shipments of any size that bring the recipient nation's inventory to more than 30 pounds of the same kind of uranium.

High enriched uranium is uranium with more than 90 percent of the isotape U-235. It is used in a wide variety of research reactors and is also the kind of uranium that can be made directly into nuclear weapons.

The Euratom countries have in the past been treated as one nation for uranium shipments. Nuclear fuel could be transferred from country to country inside Euratom, reprocessed and its plutonium extracted, all without U.S. approval.Euratom is an association of the nine nuclear electricity resources.

The Non-Proliferation Act requires all countries of Euratom to agree to strict transfer and reprocessing controls every time a nuclear export leaves the United States.

Euratom had to agree to begin renegotiating these controls 30 days after the law's enactment or face the uranium embargo that has gone into effect.

Among the 22 licenses held up is one for 154 pounds of high enriched uranium bound for two research facilities in France at work on the French fast breeder program. A shipment of plutonium to Italy, two shipments of high enriched uranium to Great Britain and 10 similar shipments to West Germany are also among those bottled up.

In the months ahead, relations between the United State and countries outside Euratom may grow strained as a result of the Non-Proliferation Act. One of the key clauses in the act requires all nuclear importing countries to agree to complete U.S. control over the reprocessing of U.S. supplied nuclear fuel in 18 months.

Spain, India, Israel, Egypt and South Africa currently cannot meet this criterion. South Africa has an enrichment plant of its own, which it refuses to put under U.S. safeguards. India has a reactor and a plutonium plant it refuses to put under outside control.

Egypt has a small research reactor outside U.S. controls, and Israel, widely reported to have nuclear arms capability, has a large research reactor at Dimona in the Negev Desert. It does not even allow U.S. diplomats to see the reactor.

Spain is a partner in a large power plant with France, which, as a nuclear weapon state, does not allow U.S. inspectors to oversee any of its facilities. The power plant is located in Spain, and the partnership with France probably precludes Madrid from meeting the requirements of the act.