In what appears to be a defiant slap at the Carter administration's human rights policy, Chile's military government has expelled three women who asked U.S. officials to help them locate missing relatives.

President Augusto Pinochet's government acted Wednesday when the women tried to return to Chile after a U.S. visit that included meetings with U.N. Ambassador Andrew Young and Terence A. Todman, assistant secretary of state for inter-American affairs.

The three women, who are Chilean citizens, were told by officials that they had been expelled and were ordered back onto an airplane bound for Buenos Aires. There, U.S. and U.N. officials helped them get a flight to New York, where they arrived Thursday.

The incident is known to have caused consternation among State Department officials. Who have been pointing, both publicly and privately, to what they regard as an improving human rights climate within Chile.

One official privately described yesterday's State Department reaction to the explusion as "astonishment and dismay."

He added that Washington's concern had been communicated to the Pinochet government yesterday, but he was unable to say what steps the administration might take to underscore its conern.

Relations, with Chile have been a controversial factor in U.S. Latin American policy ever since Pinochet came to power in a bloody 1973 coup that overthrew the Marxist generment of the late President Salvador Allende.

Chilean dissidents have charged the Pinochet government with wholesale violations of human rights, including the murder, torture and imprisonment of thousands of its foes.

Within the United States, anti-Pinochet groups have accused the Carter administration of ignoring human rights issues where Chile is concerned. These foes have been especially critical of a visit to Chile by Todman, and President Carter's reception of Pinochet when he came to Washington in September for the signing of the Panama Canal treaties.

The administration has defended these steps by arguing that it can have more effect on improving the Chilean situation if it maintains some links with the Pinochet government. In recent weeks, administration officials have cited several moves by Pinochet to ease repression as proof that this policy was working.

The victims of the expulsion order were Anna Gonzalez, Gabriela Bravo and Ulda Ortiz. They came to the United States Oct. 6 to publicize their quest for information on the fate of relatives whom they say were arrested by the Pinochet government and who have not been heard from since.

When they arrived back in Santiago Wednesday, representatives of several embassies - including those of the United States, Britain, Sweden, Austria and the Netherlands - were present to see whether Chilean officials took any action against the women.

Diplomatic sources said yesterday the embassy observers were informed that an expulsion order had been issued against the three women. The sources said however, that neither the women nor the diplomatic observers were shown the order or given any reason for it before the three were ordered aboard a flight to Argentina.