On May 6, two days after Argentina sank the British destroyer Sheffield, Ford Motor Argentina, a subsidiary of the U.S. company, announced that it was donating 60 trucks to this nation's military effort.

In a press release widely publicized here, Ford President Juan Maria Courard noted, "These units, which Ford Motor Argentina supplies to the armed forces, constitute one of the ways that our company wants to be part of this decisive moment for the country."

Not to be outdone, Union Carbide Argentina, which owns two Eveready plants here, offered $30,000 worth of flashlights and batteries to the Argentine troops. Federico A. Dodds, head of Union Carbide here, proudly posted on his factory bulletin boards a personal thank-you note from Argentina's President Leopoldo Galtieri.

"With Argentine emotion, I received your offer of the donation by your firm, which adds your effort to the regaining of the Malvinas Falkland Islands for our national inheritance," Galtieri wrote Dodds.

While the U.S. government is sending missiles to aid Britain in the war over the Falkland Islands, subsidiaries of U.S. companies here, fearful about their economic future, are providing supplies, funds and moral support to the Argentine cause.

One U.S. food company donated $50,000 worth of cheese, bouillon cubes and candy to Argentine soldiers.

"It would have been bad manners not to," said the company's president, who was solicited by an Argentine naval officer. "We look upon it as charity to the unfortunates who happen to be fighting. Besides, if I'd said no, I'd have 3,000 Argentine employes mad as hell."

The American Chamber of Commerce in Buenos Aires, representing 500 U.S. companies, sent a telegram to President Reagan May 12 condemning the "perfidious intervention by a European power in this continent, . . . the desperate effort of Mrs. Thatcher's government in trying to bolster her political fortunes by the attempted recovery for her empire and the Falkland Islands Co. of a territory whose inhabitants were treated by the British in a way that, in the United States, would have been a violation of human rights."

The chamber, whose 20-member board includes executives of companies such as Citibank, Exxon, Goodyear, Coca-Cola and Warner-Lambert, wrote Reagan that the British effort was "a malevolent cause."

"Our hearts tell us that the Malvinas Islands are a part of the Argentine heritage and must remain so," said the telegram, published in all newspapers here.

U.S. investment in Argentina reached $2.4 billion at the end of 1980, or 40 percent of all foreign investments here. Spurred by offshore oil exploration and financial investments to take advantage of a favorable exchange rate, U.S. interests here grew rapidly after the military government took power in 1976 and cracked down on the guerrilla movement. About $9 billion of Argentina's $34 billion foreign debt is reportedly owed to U.S. banks.

However, while a few executives of U.S. companies here have traveled to New York and Washington to plead for U.S. neutrality on the Falklands, there is little evidence that the headquarters of the multinational corporations are actively involved.

Does Exxon, which has large investments in Britain's North Sea, endorse the Chamber of Commerce telegram?

"We are a member of the chamber's board," said Jose Maria Cafferata, a spokesman for Esso Petrolera Argentina. "But that is a very difficult question to answer."

Esso Petrolera contributed $150,000 to the Argentina Red Cross "oriented toward those affected by the conflict." Its employes gave to the Patriotic Fund, the government's multimillion-dollar war chest, as have the employes of IBM and virtually every other American company here.

Lawrence J. Bocci, a chamber board member who represents an Ohio roller bearing manufacturer , donated money to the Patriotic Fund.

"Everyone knows the Malvinas are Argentina's," he said. "But, I wouldn't want to put my company's name on the telegram. Our investment in England is 10 times what it is here and I'm sure my counterpart in England feels equally strongly."

One exception is the First National Bank of Boston, or Banco de Boston, the largest foreign bank in Argentina, with 25 branches here. Ogden White, head of the bank's international operations, earlier this month criticized Britain's "unusual display of belligerence and the Reagan administration's backing of the United Kingdom's position of reiterated intransigence and aggression."

The Boston bank's top executives have lobbied for U.S. neutrality. Banco de Boston's general manager here, a dapper, Harvard-educated Argentine named Manuel Sacerdote traveled to the United States at the Argentine government's request.

"But the reception was fairly cold," he said, adding that the U.S. position could mean that Argentines would "decide they'd rather do business with a local bank." On May 12, a bomb exploded in the bank's Quilmes branch, but no one was hurt.

As anti-American sentiment grows following Argentine setbacks on the Falklands, a grass-roots boycott movement against British and American products is gathering strength. U.S. exports to Argentina in 1981 were about $2 billion, or 22 percent of the import market here.

A radio station in Salta, a northern city, has stopped playing English-language songs, and the Intransigent Party there circulated a boycott list naming Coca-Cola, Pepsi-Cola, Eveready, Gillette and Palmolive.

"The purchase of foreign-made consumer articles means the use of Argentine money for arms that attack and assassinate," according to a party declaration in the Salta Tribune May 9.

"Don't feed imperialist parasites!" advised a leaflet distributed by an oil workers' union in Chachapoyas. In Mendoza, a western city, a construction union demanded that 70 companies stop purchasing English and U.S. products, such as those produced by Shell and Exxon.

Casa Alvarenga, a wholesale grocery store in Formosa, a northeastern city, invited consumers in a newspaper ad to abstain from buying British and North American products to show "solidarity with the cause of national sovereignty."

Although Argentina's government has shown no signs of endorsing a boycott, and, indeed, has provided unsolicited police protection for U.S. plants here, a U.S. soft-drink company executive said, "Soon the boycotts will have a government blessing. What other way do they have to retaliate against the U.S.? The multinationals are going to be under great attack because Argentines feel the U.S. is a traitor."

U.S. companies here have experienced anti-Americanism before.

"We don't have any options but to cooperate" with the war effort, said Lawrence Daniels, second vice president of the American Chamber. "The Argentine is a very emotional creature. If you don't clarify your position, you're suspect. There could be repercussions. I remember in the '50s, if you didn't contribute to the Eva Peron Foundation, the government would shut you down."

Since April, many U.S. companies have pulled their U.S. nationals out of Argentina. However, most U.S. companies have been managed by Argentines since the guerrilla war of the 1970s. At that time, executives of Coca-Cola, Firestone, Kodak, Exxon, Amoco and Banco de Boston were kidnaped for multimillion-dollar ransoms. Two Ford executives were slain by guerrillas.

U.S. companies supported the military's severe crackdown against dissidents and still maintain warm relations with the armed forces. One soft-drink company executive said current wartime contributions are nothing new: "We've been giving to the armed services for years."

Economics aside, many U.S. company executives here take Argentina's side in the war simply because they are Argentines in a nation united in favor of Argentina's cause. One president of a U.S. company here, an Argentine, has a son fighting on the Falklands, Daniels said.

Union Carbide's Dodds is a fourth-generation Argentine of Scottish ancestry, and wears an Argentine flag in his lapel. He sees no conflict of interest in his company's gift to the Army.

"Any company in any part of the world benefits from the society it does business in. It owes that country quite a bit," he said.

Daniels, who has lived here 37 years, says, "I'm about as pro-American as you can get. My wife is a 24-bar Daughter of the American Revolution. I'm a member of the Society of Cincinnati. But Paul Revere and Sam Adams would turn over in their graves if they knew the U.S. was supporting a colonialist power."