Two Argentine Air Force officials attached to the Washington embassy were threatened earlier this month by federal officials with possible expulsion from the United States for their role in an attempt to purchase vital equipment for Argentine fighter-bombers from a California aircraft dealer.

According to U.S. and Argentine officials involved in the incident, the Argentines were seeking spare parts, particularly external fuel tanks that could increase the flight range of U.S.-built A4 Skyhawk fighter-bombers used by the Argentine Air Force in its assaults against the British fleet off the Falkland Islands.

Export of such material to Argentina is prohibited under sanctions imposed by the Reagan administration on April 30, as well as under a previous ban on the licensing of some sales to Argentina because of findings of human-rights abuses by its government. The sanctions, and U.S. military assistance to Britain, have been strongly protested by Argentina, as well as by most of the rest of Latin America.

As the Falklands conflict has intensified in recent weeks, Argentina has launched an increasingly desperate international search, primarily through sympathetic Latin American businessmen, for weapons and military supplies.

U.S. officials said they have stepped up their efforts to monitor exports to Argentina to ensure that supplies that could be used in the war are not slipping through. But exasperated Argentine officials say the crackdown is hindering even the investigation of possible future supply sources, in case sanctions are lifted, as well as legitimate business.

"We need your help," said Col. Ruben A. Corradetti, the Argentine Embassy official in charge of Air Force purchases in the United States. "I know at the moment it is close to impossible. People are afraid," Corradetti said, referring to American businssmen fearful of violating the ban.

"We don't want to go to Russia, [but] if I go to other places it is because I need it very badly," said Corradetti, who said he authorized the visit to California.

"The FBI believes I want to buy bombs here; really that is crazy," Corradetti said, adding that he is not "stupid" enough to think that his government could smuggle bombs or fuel tanks out of this country.

Corradetti said he also would like to buy U.S. ejection-seat devices that would permit Argentine pilots to bail out of A4 jets hit in combat, but the sanctions prohibit it. Corradetti said he has told top U.S. military officials that "this is against human rights. My pilots are flying in aircraft without [safety] equipment."

Even before the ban went into effect, customs officials on April 26 in San Francisco, relying on what they said were defective export licenses, seized a shipment of 32 secondhand engines purchased by the Argentine government for the A4 jets that were going to be cannibalized and used as spare parts.

A short time later, during the first week in May, two Argentine officials identified as Col. Juan Manuel Baigorria, an assistant air attache at the embassy in Washington, and Eduardo Cardetti, a technical aide, arrived in California. They were accompanied by two Florida businessmen, identified as Tomas Medina, an Argentine national living in Miami, and Hugo Gralia, also of the Miami area.

The four met in an Oakland, Calif., suburb with a dealer who specializes in modifying planes for long-range flights. The extra fuel tanks they sought, according to military analysts on both sides of the conflict, could increase significantly Argentina's offensive capabilities by enabling Argentine aircraft flying from mainland bases to reach British aircraft carriers and troop transports, such as the converted luxury liner Queen Elizabeth II, that now are out of range. They also would increase the amount of bombing time over close-in British ships for Argentine jets, which now are believed limited to one sweep before they must return to base 400 miles away.

A source familiar with the proposed fuel tank deal said the purchase was to be arranged by Medina and Gralia, who discussed paying "in the neighborhood" of $50,000 for about 50 tanks, and nothing was said about shipping them to Argentina. "Argentina was not mentioned" in the negotiations, and the money was to be paid either in cash or by a cashier's check, the source said.

However, on May 7, acting on a tip, U.S. customs and FBI agents confronted the two Argentine officials and Medina and Gralia at a San Francisco hotel, according to Justice Department and FBI officials. Medina and Gralia were told they could be criminally prosecuted, and the Argentine Embassy officials were told that they could be declared personae non gratae and expelled from the United States if they conspired to ship the tanks to Argentina covertly, federal officials said.

A State Department official involved in the decision to warn the Argentines said that "we told customs to enforce the law" and to make it clear that the fuel tanks cannot be shipped to Argentina legally.

The four men told the customs and FBI agents they were not trying to smuggle the tanks out of the United States, a Justice Department spokesman said. No formal action was taken against them, and the sale has not occurred.

Gralia, 31, said in a telephone interview that he and Medina are Argentine nationals in the export-brokering business and that they sometimes work together. He and Medina considered purchasing some of the tanks and holding them for resale until after the ban on sales to Argentina is lifted, Gralia said. "The tank for the A4, it's a hell of a big thing. No one could smuggle that out of the country," he said. Medina is currently in Spain, Gralia said.

Corradetti said Medina, whose relationship with the Argentine government he declined to discuss, had told him, "If you want some of these parts, I can buy them," and that Baigorria was sent to "check" things available, "especially the ground equipment and the tanks." Corradetti said he "didn't know if the tanks were the right type for the A4." He suggested that the Argentines were seeking nonrestricted civilian use equipment that later could be converted for military use.

"I am free here in your country" to inquire about what kind of equipment is available, Corradetti said.

Direct sales or shipments of U.S. military equipment to Argentina have been prohibited since 1978 because of U.S. findings of Argentine human-rights violations. Although the Reagan administration succeeded last December in having Congress lift the ban, any sales or licensing were made contingent on presidential certification that Argentina's human rights record had improved. Anticipating such certification (from which the seized A4 engines were exempt as obsolete), Corradetti said, he began preparing for expected purchases before the new Falklands-related sanctions were imposed.