The Reagan administration, seeking to reassure conservatives who fear it is giving the Soviet Union a policy-shaping role in Central America, moved today to dispel any idea that it wants to engage the Soviets in negotiations to end El Salvador's civil war.

Secretary of State Alexander M. Haig Jr. told a news conference here that El Salvador is "at once a global, regional and local problem," but "it does not mean we are suddenly bringing the Soviet Union into urgent matters of great significance to the hemisphere."

Haig, who on Sunday gave Mexican Foreign Minister Jorge Castaneda U.S. proposals for ending alleged Cuban and Nicaraguan intervention in El Salvador, also denied that Mexico has been empowered to negotiate with these countries on behalf of the United States.

He emphasized that there are no plans at this time for high-level U.S. talks with either Cuba or Nicaragua, and he described the proposals given to Castaneda as a reiteration of a plan offered to Nicaragua last year and rejected by the revolutionary government there.

As outlined by Haig, the points in the U.S. proposal do bear close similarities to the earlier U.S. offer. However, the version described by Haig today seemed to go further in specifying the concessions the United States would make in exchange for Nicaragua halting its aid to the leftist guerrillas in El Salvador.

According to Haig, the United States proposes:

* What would be, in effect, a nonaggression pact between this country and Nicaragua.

* A U.S. commitment to clamp down on antigovernment activities by Nicaraguan exiles in the United States.

* A regional understanding among Central American nations not to import heavy offensive weapons and to reduce the number of foreign military advisers there to low levels.

* A restoration of U.S. economic aid to Nicaragua.

In exchange, Haig said, the United States insists that Nicaragua cease all of its support, supply, training and other help to the guerrillas fighting the U.S.-backed, civilian-military government in El Salvador.

These were the points that Haig repeatedly sought to stress in a lengthy statement that he called an attempt "to put the state of play into sharper focus." It came after a series of actions by the administration in recent days that U.S. officials privately said had caused confusion and uncertainty about the steadiness of the U.S. course in dealing with Central America.

The latest problems began Saturday when an anonymous senior State Department official told reporters that the El Salvador situation was part of a global East-West struggle extending beyond Nicaragua and Cuba to the Soviet Union.

Haig, who has been here for a two-day meeting on President Reagan's Caribbean Basin initiative, made the same assertion Sunday, and at the same time gave the U.S. proposals to Castaneda. Castaneda expressed optimism that the proposals might help lead to a negotiated resolution of Washington's tensions with Cuba and Nicaragua in accordance with a peace proposal advanced by Mexican President Jose Lopez Portillo three weeks ago.

U.S. officials said the confluence of these factors, coupled with what they contended were some erroneous press reports about their meaning, had stirred speculation that the administration might be trying to find a way of disengaging from its involvement in El Salvador.

In particular, some officials acknowledged, suspicions began to surface among anticommunist conservatives, who form the hard core of Reagan's political support, that the administration might be willing to turn over its negotiating powers to Mexico or even to give the Soviets an entry into hemispheric affairs.

The officials said Haig's statement today was intended to relieve these concerns and resolve any doubts about the president's determination to safeguard U.S. interets in the region. However, it was evident from the questions asked at his news conference that considerable confusion still exists.

That policy unquestionably has taken some puzzling twists and turns in recent weeks. Washington initially reacted to the Lopez Portillo initiative with barely concealed frostiness, but since then has elevated the Mexican effort to a potentially major factor in the Central American situation.

Similarly, the sudden talk about the global dimension to the Salvador problem appears to represent a shift away from the administration's emphasis on pursuing a solution through increased military and economic aid to the Salvadoran regime.

In part, these changes are known to reflect a growing conviction within the administration that the Salvadoran guerrilllas cannot be vanquished until their outside support is cut off. As a result, Washington now seems to be putting renewed stress on seeking, through pressures and concessions, to get Nicaragua, Cuba and the larger communist world, represented by the Soviet Union, to sever their ties with the insurgents.

This stress on pursuing a solution by dealing with outside sources might also represent an attempt to convince congressional liberals, opposed to the administration's requests for increased arms aid, that Reagan is willing to seek a negotiated rather than a military settlement.

But, as today's events made clear, the administration also faces the risk that appearing to be too flexible can stir uneasiness in conservative ranks. The emphasis today was on trying to steer a tricky course between reassuring the conservatives, while still allowing probes at negotiations with Nicaragua and Cuba and possibly even discreet efforts to test the Soviet Union's willingness to use its influence.

In addition to Haig's efforts, White House deputy press secretary Larry Speakes told reporters on board Air Force One flying to Montgomery, Ala., that Reagan supports the comments made Saturday about the "globalized" nature of the Salvadoran conflict and is not unhappy about the views expressed by Haig.