Departing from the quiet diplomacy of the past, which has failed to gain desired political liberalization in Chile, U.S. officials have begun to show more open support for the country's democratic opposition in its efforts to unseat one of Latin America's last remaining military dictators.

The new U.S. stance has drawn criticism from Gen. Augusto Pinochet, who last month rebuked the new U.S. ambassador, Harry Barnes, for breaking "the minimum norms of [diplomatic] relations." Barnes has made a point since his arrival in November of contacting leading opposition figures and human rights activists, even before meeting all four members of the ruling military junta.

In another indication of his irritation with changing U.S. policy, Pinochet refused to receive visiting Sen. Edward M. Kennedy (D-Mass.), long a critic of human rights violations by the Pinochet government.

[State Department spokesman Bernard Kalb criticized the Chilean government Thursday for "inadequate" security measures during a demonstration against Kennedy when he arrived at Santiago's airport. Kalb said Washington had informed the Chilean government in advance that a progovernment group planned such a protest, but he stopped short of saying that the government mounted the demonstration. He said senior Chilean officials had expressed regret for the incident.]

How far U.S. policy has really shifted is being questioned by some opposition figures, who say American actions have been ambiguous. On the one hand, the Reagan administration strongly endorsed the National Accord signed in August by the major parties, with the exception of the Communist.

On the other hand, the U.S. government has not blocked new loans from the World Bank and other international lending institutions to the Pinochet government, which has kept current on payments of its $20 billion foreign debt. U.S. representatives, moreover, declined recently to support resolutions at the United Nations and the Organization of American States criticizing Chile's human rights record.

Such seemingly contradictory actions have blurred public perceptions of U.S. policy lines and have suggested to some here that U.S. officials may be divided over the proper posture to take in Chile's delicate political contest. Barnes is understood to have been sent to Chile with a broad mandate to define what role the United States can play in encouraging the return of democracy here.

The administration initially followed a policy of cultivating good relations with Pinochet, nudging him toward accommodation with Chile's moderate opposition on a plan for gradual return to elected civilian rule. But after tentative moves toward flexibility in 1983, Pinochet abandoned the idea of dialogue and renewed repression against strikes and leftist violence that broke out in 1984.

Many repressive measures remain in effect, and Pinochet has rejected the opposition National Accord.

Balancing U.S. concerns about human rights violations here is concern about containing Chile's sizable Communist Party. A democratically elected Marxist coalition ruled in Chile from 1970 until the 1973 coup by Pinochet.

U.S. officials have said that their hopes for Chile would not be served by an abrupt change of leadership that would heighten tensions and give the radical left an opportunity to win greater support. Washington is said to favor a negotiated transition to democracy and to prefer that it happen sooner rather than later.

The signing of the accord has been enthusiastically received by U.S. officials waiting for a sign that the splintered opposition groups could agree on a program that did not demand Pinochet's precipitous removal. The accord has provided an alternative to the military-backed 1980 constitution.