The Exxon Corp. committed itself yesterday to purchase a copper mine from the Chilean government for $107 million - easily the largest American investment in Chile since the military coup of 1973 - and declared that it intends to invest up to $1.1 billion to expand production.

It is the first major investment abroad by Exxon, the world's largest corporation, that is not in the energy field.

The Carter administration has cut off aid to Chile and criticized it sharply for alleged violations of human rights but Exxon officials pointed out that the corporation consulted the State Department before making the mine commitment.

A U.S. official, acknowledging the consultation, said Exxon was told "our policy is one of strict neutrality."

The mine bought by Exxon is La Disputada (the disputed), which was owned by French interests until was nationalized in 1971. The socialist government of President Salvador Allende bought it along with the much larger copper mines then owned by Anaconda, Kennecott and Cerro.

On overthrowing Allende 4 1/2 years ago, the presently ruling military junta vowed to overturn almost all of his policies but declared that the big copper mines would remain in government hands.

La Disputada, with an annual production of about 37,000 tons of refined copper, is considered a middle-sized mine. But investment on the scale cited by Exxon would be justified only by an increase in production that would rank in with Chile's largest. The Andean nations is the world's leading exporter of copper.

In the ceremonies in Santiago yesterday, Exxon agreed to pay the Chilean government $86 million by Feb. 1 and the balance following an audit.

Exxon executive J.J. Finley of Coral Gables, Fla., who is to become president of La Disputada, said preliminary explorations indicate "sufficient ore reserves to justify a major expansion . . . of $1.1 billion."

"I want to emphasize that our investment figure is very preliminary," he added. The text of his statement was released by Exxon in New York, where an official said in a telephone interview that the company will send $7 million on a 30 month study measuring the mine's full potential.

The investment comes at a time when world demand for copper is stagnant and the price is low. But Exxon officials indicated they are looking ahead to a resurgence in the 1980s and industry sources indicate that projection is widely shared.

Chile, having received little foreign investment since the coup, has sought to interest copper companies in several unexploited ore bodies. Kennecott and Anaconda, which received broad support from the Nixon administration in their attempts to prevent expropriation under Allende, have been among investors showing interest.

Exxon is the first to make a aommitment. Spokesman James Morakis said Exxon's only previous venture in copper began in 1976 at Crandon, Wisc., where an eventual investment of up to $400 million in copper and zinc production is foreseen.

Morakis said Exxon seeks to diversify and that its experience in resource management, acquired in oil operations, carries over into other minerals.

Diversification by oil companies figures in the U.S. debate on the Carter administration's energy policy, with critics charging that the firms are reaping windfall profits now that in turn are being diverted from development of future energy sources.

Asked if the human rights practices in Chile were considered in Exxon's investment decision. Morakis said company policy was to refuse to characterize any government. But he said stability in Chile was a strong consideration.

Last year, Undersecretary of State for Economic Affairs Richard N. Cooper told the Council of the Americas, which embraces the main American investors in Latin American, that "while in the short run it might appear opportune to support" dictatorships, "over the longer term a regime that relies upon force for its authority can be neither popular nor stable."

While he did not name Chile, is high on the department's list of a legedly dictatorial regimes.

Rights activist Laurence Birns said Exxon's move "undercuts Washington's effort to curtail rights violations in Chile" and added that his Council on Hemispheric Affairs intends to enlist church, union and consumer groups in a boycott of Exxon products to bring the point home.

La Disputada takes its name from past conflicts over title to the mine, perched several thousand feet high in a nearly inaccessible ridge of the Andes 40 miles north of Santiago.

It is said that the ore body was found by two prospectors approaching independents from opposite sides of the mountain - and hence the first of what have been recurrent disputes.