Exild or out-of-power Latin Americans have begun turning up in Washington, hoping to take advantage of President Carter's well-publicized interest in human rights.

Most can count on seeing such State Department officials as Assistant Secretary for Inter-American Affairs Terence Todman, Human Rights coordinator Patricia Derian or her deptty, Mark Schneider, who formerly received such delegations as an aide to Sen. Edward M. Kennedy (D-Mass).

The visitors express appreciation for the official receptivity, a contrast with the cool years of the previous administrations, when the only audience an even mildly leftist Latin American could expect was with a handful of congressional advocates of human rights.

But often the visitors seem more enthusiastic about the Carter administration's potential for helping their cause than for its actual achievements.

Luis A. Siles Salinas, a once and possibly future president of Bolivia, was typical. Obviously pleased to meet with Deputy Secretary of State Warren Christopher last week, Siles nevertheless declared that the most tangible result of Carter's rights advocacy - promises from several Latin dictators of eventual elections - "is really just another fraud."

Siles, 52, was president of Bolivia for six months in 1969 before falling in one of the Andean nation's then frequent coups. In recent years he has headed a human rights campaign that "through habeas corpus cases and publicity" has become the only effective check, he contends, on the military rule of President Hugo Banzer.

The views of Siles reinforced those expressed here by another visitor, Juan Jose Arevalo, president of Guatemala from 1945 to 1950 and frequent target then of coup attempts that he blames on U.S. supported interests.

During long years of exile, Arevalo had never visited Washington. At the invitation of the Organization of American States, he came for a lecture tour and met with members of Carter's early team on Latin American policy.

Arevalo wrote a book about the overwhelming weight of U.S. influence in the Caribbean, calling it "The Shark and the Sardines." The book was widely read in Latin America and an English translation, published in 1961, had an impact on the Latin American policy of President Kennedy.

Despite a renaissance of representative government in the area at that time, several military coups soon shifted the balance. According to Arevalo, U.S. influence again propped up the ruling generals.

Arevalo's message to official Washington: "The United States inevitably intervenes in Latin America. Let that intervention be for democracy, let it be on the side of the people."

Arevalo, 73, is again living in Guatemala, where elections are promised next year, but he says he is too old to run.

Another exiled Central American, Christian Democratic leader Napoleon Duarte of El Salvador, visited Washington early this year to warn against fraud in presidential elections that were held shortly after his visit.

Duarte had his picture taken with Vice President Mondale and saw numerous sympathetic officials.

As Duarte predicted, the ruling military's candidate won the elections and there were widespread charges of fraud. In an unprecedented move, a U.S. House subcommittee held a hearing on the charges.

Duarte remains in exile, but U.S. comments on a series of alleged human rights violations following the El Salvador elections are widely credited with lessening tensions there.

The point that former Bolivian President Siles attempts to make in Washington is that elections permitted and held by a ruling military power are unlikely to change thins in any country.

The biggest enemy of democracy in Latin America, he said, "is not communism or fascism bu false democracy" manipulated by entrenched interests.

Banzer in the expected official candidate in next year's election and the opposition hopes Siles will run.