El Salvador's vice president told Secretary of State Alexander M. Haig Jr. yesterday that the Central American country's military forces are definitely committed to stand by the results of the constituent assembly elections March 28.

The statement by Gen. Jaime Abdul Gutierrez, one of El Salvador's most powerful military leaders and the No. 2 man in civil office, was reported by diplomatic sources after his midday meeting with Haig at the State Department.

There was no discussion in the meeting, according to the sources, of possible negotiations between Salvadoran junta leaders and leaders of the Salvadoran insurgency.

The Reagan administration has received appeals from several sources, including Mexican President Jose Lopez Portillo and 104 members of the U.S. House of Representatives, to back such negotiations as a means of ending the Salvadoran civil war.

Last Thursday, in a more ambiguous move along the same lines, the House approved a non-binding resolution, 396 to 3, urging the administration to press for "unconditional discussions among the major political factions in El Salvador in order to guarantee a safe and stable environment for free and open democratic elections."

Haig is expected to discuss the Mexican appeal today in a New York meeting with Mexican Foreign Minister Jorge Castaneda.

One of the central obstacles to Salvadoran negotiations is believed to be the strong opposition of the military leadership there. Haig's silence on this subject in the meeting with Gutierrez suggests that no U.S. push toward negotiations is under active consideration.

The political development in El Salvador being watched with the greatest intensity and suspense by U.S. officials is the balloting March 28 for a constituent assembly.

Officials have made no secret of their hope that the election will strengthen the position of President Jose Napoleon Duarte and his Christian Democrats, who are somewhere in the middle of the political spectrum.

Some political observers here and in Central America have expressed concern, however, that the elections might strengthen forces of the far right and weaken Duarte.

In an interview last Saturday with The Washington Post, Haig said such a result would be "unfortunate," but that "we would be prepared to live with that" or any other results, if the electoral process seems fair.

Gutierrez, according to the sources, was here for a short visit en route home from a mission to Taiwan in connection with a $3 million Taiwanese economic development plan for El Salvador. The Salvadoran vice president also saw Secretary of Defense Caspar W. Weinberger and other defense officials yesterday.

Haig promised a House Appropriations subcommittee Thursday that he would produce evidence soon, possibly as early as yesterday, to back up his charges of Cuban and Nicaraguan interference in the Salvadoran fighting.

Although some highly classified information had been presented earlier to the Senate and House intelligence oversight committees, government officials did not produce a version for wider distribution yesterday, although they said work on such a presentation is continuing.

Intelligence agencies are reported willing to provide information to the public about the military buildup within Nicaragua and about Nicaraguan military actions against the Miskito Indians near the Nicaraguan border with Honduras.

But details to back charges of Nicaraguan involvement in El Salvador, as well as charges of Cuban and even Soviet participation, are considered so sensitive that an extensive report seems unlikely, officials said.

In a related development, the commander of the U.S. Atlantic Fleet testified yesterday that the fleet's contingency plans have been revised during the last year to meet the "expanding military influence of Soviet-supported Cuba in Central America."

Adm. Harry Train also told the Senate military preparedness subcommittee that "we have shifted the center of the Atlantic Fleet training activity to the Caribbean" because of an increased Cuban threat.