Over anguished objections from the U.S. Navy, President Carter has blocked anti-communist Chile's participation in the 21st annual inter-American naval exercises this fall -- continuing the administration's unqiue policy of meeting the march of communism in the Western Hemisphere.

Appeals by the Navy and prominent members of Congress have not budged the president. His policy in this instance is inflexible: official U.S. hostility toward Chile's military regime will continue as long as Chileans accused of complicity in the Washington assassination of former foreign minister Orlando Letelier are neither extradited nor prosecuted.

But transcending the lingering Letelier affair is Carter's overriding Latin policy, seemingly unaffected by the end of detente. At the same time that Carter was punishing Chile, he was bowing to demands by leftist President Aristedes Royo of Panama that the United States call off its planned amphibious operations at Guantanamo -- a demand echoing Fidel Castro's position.

The message for Latin Americans is unmistakable: anti-communist policy in no way mitigates State Department complaints against right-wing authoritarian regimes. In contrast, whatever their shortcomings in human rights, leftist authoritarian regimes are blessed with U.S. deference (as with Panama) and aid (as with Nicaragua's new Marxist dictatorship).

Administration foes of Chile's military government, which toppled the country's Marxist regime in 1973, have artfully exploited the Letelier assassination. The Chilean supreme court, citing insufficient evidence supplied by the United States, has refused to extradite or prosecute three Chilean secret police agents accused by the United States of planning the 1976 slaying. Letelier, foreign minister of the Marxist regime, kept close ties to Cuba and East Germany as a Washington-based exile.

In retaliation, the United States has cut back its diplomatic presence in Chile, drastically reduced military ties and banned economic development loans. Had the same standards been applied to activities of Soviet thugs here and elsewhere, diplomatic intercourse between the West and Moscow would be impossible.

On April 15, Treasury Secretary G. William Miller killed a $32 million "basic human needs" loan for Chile from the World Bank. On that same day, the United States vetoed a $43.5 million farm-credit loan and a $32 million highway loan to Chile. All this was predicated on the Letelier case.

So was the State Department's decision in early May to exclude Chile from the inter-American naval exercises -- the first time such a step had ever been take for political reasons. The U.S. Navy appealed the decision, arguging that increased U.S. activity in the Persian Gulf and Indian Ocean with a depleted fleet made cooperation with allies essential; Chile's navy, patrolling a 2,600-mile coastline, is one of the hemisphere's best. Defense Secretary Harold Brown rejected the appeal.

Soon after, the Pentagon indefinitely postponed the amphibious exercises scheduled off the U.S. naval base at Guantanamo. The avowed reason was the need of U.S. naval warships to help the Cuban refugee fleet to Florida. But one well-placed admiral privately says that is nonsense; the Pentagon was bowing to pressure.

Pressure by the State Department was applied from the moment the amphibious exercises were scheduled; officials there feared that U.S. naval activity would provoke Cuba and its Caribbean friends. In a May 3 telegram to Carter made public in Panama City, President Royo called for cancellation of the exercise in words that echoed Havana's position: the Caribbean "has ceased to be the private sea of the United States."

Nothing could be done but the postponed amphibious exercises, but the Navy quietly mobilized an impressive bipartisan corps of senators and House members to protest the Chilean exclusion. Their letters to the president drew a uniform response: silence. The White House has not even bothered to explain the Letelier connection.

These unanswered letters stress the strategic wartime danger of defending Cape Horn shipping lanes without a cooperative Chilean navy. In a separate personal letter to Secretary of State Edmund Muskie, also unanswered, Sen. Richard Lagar of Indiana questioned how excluding Chile from the naval exercises can help "the cause of human rights in Chile."

But is the administration's Latin policy really all that concerned with improving human rights in Chile? A recent "confidential" telegram to embassies from the State Department, revealing further U.S. steps against Chile, conceded "improvements in the [Chilean] human-rights situation." Only the Letelier case is cited to justify the pro-left, anti-right U.S. tilt in Chile at a moment when the tide of communism creeps steadily higher in Latin America.