Americans may be edging back toward mediator's role

Again the US appears to be acting as a catalyst for fresh diplomacy to solve the Falklands crisis, despite Washington's clear tilt toward Britain in the dispute.

London's initial reaction to a joint US-Peruvian peace plan is said by British officials to be ''constructive.''

The proposal, first offered by the president of Peru and then apparently refined by Secretary of State Alexander M. Haig Jr., is separate from suggestions put forth by UN Secretary General Javier Perez de Cuellar.

At this writing Mr. Perez de Cuellar was awaiting replies to his proposal from Argentina and Britain. The UN plan reportedly calls for a cease-fire and a mutual withdrawl of Argentine and British forces.

The Falkland Islands, with their 1,800 inhabitants, then would be administered by UN officials while Britain and Argentina negotiated the islands' future.

How the US-Peruvian plan differs from Mr. Perez de Cuellar's proposal is not yet clear. Peru, meanwhile, is seeking an Argentine response to the latest initiative, while London channels its views through Mr. Haig.

Indeed, a high Argentine official lashed out angrily Wednesday at what he termed the ''spurious colonial alliance'' of the US with Britain. The United States, said Argentine ambassador to the UN Eduardo Roca, is ''as responsible as the British for the fighting.''

''The Argentine people will never understand or forget,'' he said, ''that in one of the more critical hours of the hemisphere's history, the United States has chosen to side with a power foreign to this hemisphere and (to help) its aggressive schemes.''

The apparent intent of the Argentine regime is to convince other Latins that the Reagan administration, despite its avowed concern for hemispheric affairs, throws its weight behind an outside ''colonial'' power.

Clearly, if the latest Haig initiative is to succeed, Argentina and Britain both would have to accept it as a basis for a cease-fire and renewed negotiations. The new flurry of diplomatic activity, following the collapse of Mr. Haig's earlier mediation mission, reflects alarm throughout the world that the shooting war has escalated to the point that hundreds of men have been killed.

The US position in the rapidly changing Falklands crisis is ambiguous. On the one hand, the US has aligned itself with Britain, including a pledge of limited American assistance to the British war effort. So far that aid appears to be confined to intelligence-sharing and an offer to refuel and resupply British units. US officials deny that the United States will be drawn into direct military operations.

On the other hand, Mr. Haig is trying to reassume a neutral role, by offering an initiative that both sides might accept as a starting point for negotiations.

To this point, Argentine President Leopoldo Galtieri insists that Argentina's troops will remain on the Falkland Islands, until London acknowledges Argentina's sovereignty over the disputed territory. Britain replies that negotiations can begin, only after an Argentine evacuation.

Presumably the Haig-Peruvian initiative somehow sidesteps this sticking point. Otherwise Prime Minister Margaret Thatcher's government would not describe the proposal as ''constructive.''

Pending a cease-fire agreement, the Falklands crisis -- now more than a month old -- continues to slip through the cracks of the elaborate peacekeeping machinery established by the world community since World War II.

The result, says Prof. Riordan Roett, director of Latin American studies at the School of Advance International Studies of Johns Hopkins, is ''one of the gravest situations in decades, with international machinery unable to pull the combatants apart.''

The United Nations so far has been ineffective. ''The Organization of American States,'' says Dr. Roett, ''has been sidelined. The World Court has not been brought in, nor has a panel of foreign ministers to mediate.''

Neither the NATO alliance, to which the US and Britain belong, nor the Rio Treaty of 1947, of which Argentina and the United States are members, seems applicable to the crisis.

Almost certainly, when the Falklands problem is solved, both the OAS and the Rio Treaty will be reexamined by the US and other hemispheric nations.

The longer the war goes on, meanwhile, and the more involved with Britain Washington becomes, the harder it will be, analysts agree, for the administration to pick up the pieces of its Latin American policy.