Argentina tonight called the U.S. move to support Britain in the Falkland Islands crisis "unjustified and intemperate" and bitterly criticized Britain as "solely responsible" for the failure of diplomatic negotiations.

A six-page communique distributed by Interior Minister Alfredo Saint Jean charged that the U.S. announcement of sanctions against Argentina "seems to be adjusted to the timing fixed by the British fleet for its operations." It said that Argentina "continues to be open to negotiation and dialogue" but was prepared "to defend itself with all the resources at its disposal."

Britain began enforcing a total blockade of air and sea within 200 miles of the Falklands, but by nightfall there were no reports of violations by Argentine planes or ships. Argentina has threatened to attack British forces in the same zone around the islands and within 200 miles of the Argentine mainland, but no fighting was reported.

Argentine Foreign Minister Nicanor Costa Mendez said his country was willing to comply with a U.N. Security Council resolution calling for immediate withdrawal of its forces from the Falklands, but he continued to insist that Argentine sovereignty over the islands was nonnegotiable, Washington Post special correspondent Michael J. Berlin reported from the United Nations.

British diplomats scoffed at the Argentine offer as an attempt to "stand the U.N. resolution on its head" by fixing terms for negotiations before withdrawing.

U.N. Secretary General Javier Perez de Cuellar offered to replace U.S. Secretary of State Alexander M. Haig Jr. as a mediator in the dispute, but only if both sides accepted, a U.N. spokesman said. Britain said it had not made such a request for the present.

The Argentine communique, the most extensive public statement issued by the government on the crisis since it invaded and seized the Falklands on April 2, accused the United States of favoring Britain during shuttle diplomacy by Haig. It reiterated Argentina's intention to maintain its claim of sovereignty and charged that the United States was failing to recognize the resolution on the dispute recently adopted by signatories of the Inter-American Treaty of Reciprocal Assistance, or Rio Treaty.

Government officials said that Argentina would not soften its negotiating stance in response to the U.S. move and sought to minimize the possible effects of the sanctions on Argentina's already crippled economy.

"We don't have any requests for loans from the U.S. Export-Import Bank, and we don't import basic products from the United States," Economics Minister Roberto Alemann told reporters. He called the sanctions "innocuous."

Diplomatic officials said they were surprised by the severity of the U.S. statement. They said Argentina had hoped to prevent an expected U.S. tilt toward Britain by avoiding an outright rejection of the last U.S. diplomatic proposals and by expressing their willingness to continue negotiations.

Argentine government sources said that the junta, while open to new talks, still expected that a battle with the British task force in the South Atlantic could begin at any time.

The Argentine statement was approved by the military junta in a meeting tonight and was released about eight hours after Haig's statement announcing the sanctions and indicating that Argentina had rejected a final U.S. proposal for solving the standoff with Britain.

The communique denied that Argentina had turned down the proposal and contained a lengthy Argentine version of Haig's three-week negotiating effort in Buenos Aires, London and Washington.

Blame for the negotiations' failure, the statement says, lies not with Argentina but in the "rigidity" and "inflexibility" of Britain.

"The British government has had no intention of accepting any agreement that signifies anything other than the renouncement by Argentina of its rights," the statement said.

"Facing the rigidity of the government of the United Kingdom, the efforts of Haig had to be turned more and more toward trying to obtain the maximum flexibility from the Argentine government in order to satisfy Britain's position . . . as the privileged ally of the United States," the government charged.

Argentine political and labor leaders quickly attacked the shift in the U.S. position. They had previously criticized the junta's cooperation with U.S. diplomatic efforts and charged that the United States was working for Britain's interests.

There were no signs tonight of retaliation against American interests in Argentina. U.S. Embassy officials, who have already received one bomb threat and shipped some sensitive documents out of the country, said no additional security measures had been taken.

Government officials said Costa Mendez's offer at the United Nations did not mark a change in Argentina's negotiating position but reflected an openness to possible U.N. mediation.

Another diplomatic move being considered by Argentina was to seek sanctions against Britain from the 21 American nations that are voting signatories to the Rio Treaty.

Rio Treaty members voted 17-0 Wednesday at the Organization of American States in Washington to approve a resolution sought by Argentina that recognized its sovereignty over the Falklands and the dependent South Georgia and South Sandwich island chains east of the Falklands. The United States and three other countries abstained.

The U.S. sanctions came as Argentina's economy is suffering from a deep recession, an annual inflation rate of 140 percent and a financial crisis that has caused numerous bank failures.

Official sources maintained that the government had been prepared for U.S. sanctions and had anticipated them with the announcement of several emergency measures this morning. Shortly before the U.S. announcement, the central bank prohibited all trading of foreign currency in Argentina without prior government approval. Previously, Argentina had banned the purchase of foreign currency in an effort to preserve its shrinking financial reserves but had continued to allow the purchase of Argentine pesos with dollars and other foreign currencies.

A government official confirmed that a plan was under consideration for special subsidies to Argentine exports. Many exporters of meat and fruit have already been hit hard by bans on Argentine imports imposed by the European Community, Australia and Canada in support of Britain in the dispute.

Last year Argentina conducted an estimated $2.3 billion in trade with the United States, according to diplomatic reports available here. This represented 6 percent of Argentina's total exports and 18 percent of its imports.

The main Argentine imports from the United States are aircraft, engineering and heavy construction equipment, trucks and other heavy vehicles and chemical products.

Diplomatic sources said that Argentina, which was cut off from U.S. arms sales in 1977 by the Carter administration over human rights violations, had no outstanding arms delivery contracts with the United States. The new U.S. measures against arms deliveries, officials said, would only affect a $50,000 appropriation for military training included in next year's budget but not yet approved by Congress.

Ten soldiers were killed when a helicopter crashed near a bay along the coast south of the port of Comodoro Rivadavia during a training mission, an Army communique said. The deaths raised to 16 the number of Argentines that the military has acknowledged have died in various incidents since the confrontation with Britain began.The military joint chiefs of staff issued a long list of guidelines for Argentine and foreign reporters under a censorship decree issued last night.

The guidelines said that Argentine and foreign news organizations should not distribute information that refers to military operations without citing an official source, speculate on the possible outcome of military confrontations or refer to military units. Other guidelines prohibited information that "produces panic," "contradicts or lessens the credibility of official information" or "undermines the belief in Argentine rights."

In the censorship law, the junta said that directors of media found to be violating the new rules could be jailed and their operations closed.

Berlin also reported from the United Nations:

There was no indication that either Argentina or Britain wanted the Security Council to resume its deliberations on the Falklands immediately.

Most diplomats here expected that the United Nations would eventually step into the mediating vacuum, but it was unclear whether a U.N. move would be possible before fighting begins.

The Argentine offer to comply with the U.N. resolution, which came just moments after Haig's statement, caused an initial flurry of reports that it might constitute a diplomatic breakthrough.

Costa Mendez told reporters after meeting Perez: "I have said that Argentina has been, and is ready now, to comply with Resolution 502 adopted by the Security Council one day after Argentina's invasion of the islands in its entirety and also willing to accept the intervention of the U.N. through any of its organs."

It was believed to be the first public expression by Argentina that it would comply with the resolution, which calls for an immediate ceasefire in the South Atlantic, an immediate Argentine withdrawal from the Falklands and diplomatic negotiations by Britain and Argentina.

But Costa Mendez repeatedly ducked reporters' questions about whether compliance would mean an immediate Argentine troop withdrawal. He also said that, under the U.N. resolution, "any negotiations should take as the principal base the Argentine sovereignty on the islands. This is nonnegotiable."

British diplomats told reporters that the Argentine statement on sovereignty, by setting terms for negotiations in advance, appeared to nullify its acceptance of the resolution.

"They're doing it in the wrong order," said British Ambassador Anthony Parsons. Argentina, he said, apparently was willing to consider withdrawal only after negotiations and a cease-fire. Asked whether he was encouraged by the Argentine offer, Parsons said, "I'd be extremely encouraged if they started withdrawal tomorrow."

Most Western diplomats here saw the Costa Mendez offer as an attempt to demonstrate to international opinion that, despite the American statement, it was Britain and not Argentina that was unwilling to negotiate.

Perez, in an interview granted here to the Spanish newspaper El Pais, was quoted as saying that a mediation effort would be very difficult without both parties' consent.

"If I offer my services and am told, 'Well, sir, we do not accept you,' then I am not the only loser, but the office of secretary general is also affected," Perez was quoted as saying.