The Reagan administration is dealing with El Salvador as "a global problem" originating in Moscow that must be resolved with a global strategy engaging the interests and vulnerabilities of the Soviet Union, a senior State Department official told reporters yesterday.

The official, who spoke at a background briefing for State Department correspondents on condition that he not be quoted by name, explained some of the thinking behind recent public statements by Secretary of State Alexander M. Haig Jr.

The official also responded to reports, which he strongly denied, that reverses on the ground in El Salvador and other parts of Central America are forcing the administration to shift toward regional negotiations as a way out of a deepening quagmire.

Haig has charged since the early days of the administration that the confict in El Salvador is part of a "global communist campaign" and he threatened over a year ago to "go to the source," meaning Cuba, in order to thwart it. The remarks yesterday gave renewed emphasis to the global aspects as the dominant issue for American policy and were more explicit than before about the central importance of the Soviet Union in the hemispheric struggle.

Asked if it is possible to persuade the Soviets to "back off" supplying Cuba and the Cubans to pull back from Central America, the official replied, "I'm suggesting you don't have the luxury of dealing with this problem in any other way."

In deciding to seek global solutions rather than to concentrate on local conditions in El Salvador, according to this official, the administration is seeking to avoid circumstances and results similar to those a decade ago in Vietnam.

"It was a terribly misleading and specious approach" to the struggle in Vietnam, reporters were told, to fight to win it on the ground through military efforts in that country and political efforts to win the hearts and minds of Vietnamese.

Instead the official suggested that a much broader program of "geopolitical leverage" against the Soviet Union and its allies should have been carried out to win the struggle in Vietnam, which he described as "a global problem that we mismanaged due to a local preoccupation."

To treat El Salvador in its own local terms, especially in view of Cuban and Nicaraguan backing for guerrillas there, would be to court creeping American escalation and increasing U.S. involvement, as in the case of Vietnam.

"Let me tell you: the president's policy is to avoid precisely that, and to deal with this issue as a global problem.

"That means we have to harness, and we have been, the full panoply of political, economic and security assets of the United States to deal with this problem in Moscow, in Havana, in the regional context of the Organization of American States and in El Salvador itself.

"The Salvadoran aspect is only a small, admittedly high-profile, very visible picture, but it is not our approach," the senior State Department official said.

The official declined to provide details of the means by which the "global solution" is being sought. Rejecting the idea that the United States is seeking a global showdown over El Salvador, he said that "the Soviet Union has certain interests and certain vulnerabilities" and the United States has "political, economic and security assets" to deal with them in a way that could force a basic shift in Soviet policy of "interventionism" in various parts of the world.

Among the Soviet interests that could come into play, the official suggested, are the need for Western technology and trade and the desire for a stabilization of the arms race and a political dialogue with the United States.

The vulnerabilities, according to this account, include the Soviet position as guardian of a troubled status quo against "a liberation movement" in Poland and "a revolutionary movement" in Afghanistan.

The official hinted that the United States has utilized or will utilize such potential pressure points, at least in discussions with Soviet officials. In this respect, he indicated, the Soviets could be asked to consider the consequences if the United States were to feel free to intervene "within your traditional sphere of influence or even areas of strategic importance to you that are not in that sphere."

"I don't mean to suggest that we'll start subverting Poland," reporters were told. "But it must be a recognized vulnerability in Moscow."

Some of the Soviet vulnerabilities are internal, reporters were told, including an emerging struggle over the succession to President Leonid Brezhnev. The official said Konstantin U. Chernenko, who is considered the heir apparent, may have been "the triggering mechanism" for recent political maneuvering against Brezhnev.

A fundamental question regarding Central America, according to the official, is whether Cuba will be able to "continue an insurgency offensive" involving the militarization of Nicaragua as well as promotion of insurgencies in El Salvador and other nearby states.

To cope with the Cuban dimension, President Reagan recently ordered an increase in U.S. military maneuvers and other forms of obvious military preparedness in the Caribbean, as well as the drawing up of contingency plans, which were announced publicly by Pentagon officials, for direct U.S. military action against Cuba in unspecified circumstances.

Mexican President Jose Lopez Portillo has proposed U.S.-Cuban negotiations as a centerpiece of a regional political solution of the increasingly explosive situation in Central America.

Haig, who is to meet Mexican Foreign Minister Jorge Castaneda in New York today on this subject, has asked that the proposal be amended to include a clear prohibition of Nicaraguan intervention in the affairs of its neighbors.