As President Jose Napoleon Duarte's Christian Democratic Party heads toward legislative and municipal elections at the end of this month, the U.S. government appears to have dropped much of the support that it provided Duarte in last year's presidential elections.

Ambassador Thomas Pickering said in an interview that the U.S. government, including the CIA, was "not supporting or opposing any party in any way" this time. Last year, it reportedly helped finance Duate's campaign.

In addition, the U.S.-funded American Institute for Free Labor Development, or AIFLD, has actively promoted formation of a new national labor confederation that would displace the existing organization allied with Duarte.

Resistance on the part of several large unions to formation of the new confederation has held up arrival of $150,000 offered by two senior AIFLD officials to finance pro-Christian Democratic union activities in the current campaign, union leaders said. An AIFLD spokesman said such an offer was "hardly likely."

The apparent U.S. shift chiefly benefits the Christian Democrats' two largest conservative opponents in the elections, the right-wing Nationalist Republican Alliance and the National Conciliation Party. They have formed an electoral coalition for the first time and together with smaller conservative parties are generally expected to retain their majority in the Legislative Assembly.

Both the U.S. administration and Congress have supported Duarte, El Salvador's first elected civilian president in 50 years, with increased military and economic aid since his inauguration June 1. But several signals suggest U.S. complacency with the prospect of a conservative victory on March 31.

The administration and embassy seem to think that a conservative victory would encourage Salvadoran rightists to pursue parliamentary and democratic tactics, and thus wean some of them away from violence, Salvadoran and U.S. political observers said.

A conservative-dominated assembly also would continue to brake any leftward moves by Duarte and thus help to preserve the political equilibrium here, they said.

Labor leaders opposed to the U.S.-backed union confederation, and some Christian Democratic Party activists, complained that the U.S. shift was undermining Duarte's declared goals of achieving a negotiated settlement of this nation's five-year civil war, prosecuting past human rights violators, and carrying out social and economic change.

"The gringos are afraid of pressure from the people and don't want the Christian Democrats to win 31 seats," a majority in the assembly, said Orlando Arevalo, president of the 75,000-member peasant union Acopai and an adviser to the Agriculture Ministry.

A left-leaning Salvadoran academic researcher said: "It seems that the American Embassy is interested in buying political stability as fast as possible. Its view is that a majority of any single party would be a threat to this incipient democracy."

Following are signs of a modest U.S. shift away from Duarte in recent months:

The CIA channeled between $1 million and $2 million of assistance to Salvadoran political parties in last year's two-round election, mostly on Duarte's behalf, according to administration and congressional sources. But this year, Pickering said, the United States is "not supporting or opposing any party in any way." Asked if this statement applied to covert CIA support, Pickering said it "applies to the entire policy of the entire U.S. government."

The revelations indicating CIA assistance a year ago embarrassed both Duarte and the U.S. government.

U.S. Embassy officials were quoted anonymously in U.S. newspaper reports last month as saying the embassy favored a conservative victory to preserve the right's stake in the democratic process, leading Duarte to demand an explanation from Pickering.

Both officials said in recent interviews that they patched up the dispute in a subsequent meeting, where the ambassador assured the president that the U.S. government was neutral. Nevertheless, the incident appeared to reflect both the embassy's and Duarte's moods regarding the elections, observers said.

AIFLD clearly has shifted its support from the Popular Democratic Union to the three-month-old confederation, called the Democratic Workers' Exchange, according to union leaders.

The Popular Democratic Union is conservatively estimated to include unions with a total of 300,000 members, including agricultural, industrial and service workers. It signed a "social pact" with the Christian Democrats in September 1983, and $200,000 from AIFLD and other, unidentified U.S. sources were channeled through it last year to help Duarte's campaign, union leaders said.

Three months after Duarte's inauguration, leaders of some of the five member unions issued a communique charging the government with lack of progress in several areas, including human rights and dialogue with the left-wing guerrillas.

Supporters of the communique said they received protests from AIFLD, the armed forces and the Christian Democrats. AIFLD's director for El Salvador, Bernard Packer, and Salvadoran labor leaders close to him then began promoting the Democratic Workers' Exchange, founded in December.

It was to include the largest four of the established confederation's five unions, plus several smaller unions linked to conservative political parties.

AIFLD wields considerable influence over the Popular Democratic Union as it pays more than half of the member unions' operating expenses. AIFLD has provided about $1.6 million to Salvadoran unions in the last 18 months, mostly to pay salaries of organizers and technical personnel, said AIFLD and union sources.

AIFLD is funded principally by the U.S. Agency for International Development and nominally by the AFL-CIO. Its chief of information services in Washington, Jack Heberle, said by telephone that the new confederation has the "primary purpose of obtaining better wages, hours and working conditions for its members," and added: "We have encouraged it. We have looked upon it as a direction in which Salvadoran unions should go." He said the purpose of the confederation aligned with the Christian Democrats "was to have a voice on political affairs."

Three of its five unions, however, are resisting joining the new confederation. They are the Acopai peasant union, an Indian artisans' union with 60,000 members and a 30,000-member state employes' union.

Leaders of the three unions said that the local AIFLD director, Packer, either had withdrawn or threatened to withdraw financial and logistical support from their organizations in the past four months to pressure them to join the new confederation.

Packer recently was reassigned to Guatemala after several union leaders demanded his resignation in a Jan. 21 letter to AIFLD chief William Doherty.