In a new effort to ease tensions with Nicaragua, the United States has offered to consider renewed economic aid if the revolutionary government will halt assistance to leftist guerrillas in El Salvador, a senior State Department official said yesterday.

The official, who declined to be identified, said an eight-point plan, expanding and making more explicit earlier U.S. proposals, was presented to Nicaragua's Sandinista-dominated government Thursday by the U.S. ambassador in Managua, Anthony Quainton. Nicaragua responded yesterday by calling the U.S. move "a positive gesture." That, coupled with the fact that both sides said the Managua meeting had gone well, appeared to indicate the drive to begin negotiations may soon reach the talk stage. Secretary of State Alexander M. Haig Jr., responding to a suggestion by Mexican President Jose Lopez Portillo, said last month that the United States is willing to initiate discussions.

But progress toward the bargaining table had been held up by U.S. insistence on awaiting results of El Salvador's assembly elections and more recently by uncertainty about the composition of the new Salvadoran government.

The U.S. official said he was unable to specify when or where negotiations might begin. Thomas O. Enders, assistant secretary of state for inter-American affairs who is expected to represent the United States, is traveling with Haig on his mission to try to avert a British-Argentine clash over the Falkland Islands.

And Nicaraguan Foreign Minister Miguel D'Escoto is expected to be at a nonaligned nations meeting in Kuwait until Thursday.

The official also stressed that he was not "extraordinarily optimistic" on chances of an agreement emerging from negotiations.

The Reagan administration privately has taken the position that, while it will keep an open mind, it does not hold much hope for success and is taking the negotiations route as a concession to Mexico and to protect itself against charges by congressional critics that it is interested only in a military solution to the Salvadoran civil war.

As described by the official yesterday, the latest American proposals follow the general lines of a plan the administration unsuccessfully offered Nicaragua twice since last summer. It involves these provisions:

An end to Nicaraguan support for insurgents in El Salvador and other neighboring countries. The official described this as as the "sine qua non," or "absolute necessity," for the United States, which contends that the Salvadoran guerrillas' continued ability to wage war against the U.S.-backed authorities there depends on the arms, direction and other support they receive from Nicaragua.

A "political declaration" by the United States making clear intentions to enforce provisions of the Neutrality Act that make it a crime to launch or plan invasions of other countries from U.S. territory.

Although the official did not discuss reports that the United States has prepared plans for covert action against Nicaragua, he acknowledged that the purpose of such a statement would be to ease Nicaraguan fears about the activities of anti-Sandinista Nicaraguan exiles in this country.

A joint statement by the United States and Nicaragua pledging not to interfere in each other's affairs or those of other countries in the Central American and Caribbean region.

An agreement for a regional ban on importation of offensive heavy weapons and a reduction in the armed forces and the foreign military advisers in the area. The official noted this would require involvement and negotiation by other Central American countries.

And he conceded that the United States intends for it to apply not to the about 45 American military "trainers" in El Salvador but to the more than 2,000 Cubans and others estimated to be in Nicaragua.

An international verification system, possibly to be administered by the Organization of American States, to check ports, airfields and other locations in Nicaragua and neighboring countries to ensure they are not being used for arms shipments. This suggestion by Honduras had not been proposed by the United States before.

Movement toward renewed economic cooperation, with the United States being prepared to ask Congress to resume direct financial aid to Nicaragua and to make it eligible to share in the trade and investment benefits of President Reagan's proposed Caribbean Basin initiative.

Cultural and human exchanges between the United States and Nicaragua as a means of building confidence in each other's intentions.

The Nicaraguan government's continued commitment, in line with earlier pledges, to permit "political pluralism," a mixed economy and nonalignment in foreign affairs as "a determinant of future relations" with the United States.

Although this was a clear reference to U.S. concern that Nicaragua is moving toward a one-party, Marxist system on the Cuban model, the official would not say whether the United States insists on Nicaragua following a political course deemed acceptable to Washington to obtain aid and trade benefits.