Wide gulf separates contra and Sandinista peace plans. CENTRAL AMERICA'S HOT SPOTS. Four months into the peace process, the region's most troubled countries show signs of change. Today Nicaragua's warring parties begin cease-fire talks. And in El Salvador, a leftist rebel leader's short visit home has transformed the political terrain.

As they launch their first round of peace talks here today, Nicaragua's Sandinista government and the contra rebels appear to be transmitting on different wavelengths. The gulf between the two sides, to judge by their respective cease-fire proposals, is not merely a matter of degree. It goes to the heart of what the negotiations are for.

The Sandinistas are seeking merely an end to hostilities and agreement on how the contra forces will hand in their weapons and return to civilian life.

The rebels are offering a five-week truce (beginning Dec. 8 and ending Jan. 17), but making it conditional on sweeping political changes in the nature of the Nicaraguan government that go far beyond the reforms required by Central America's peace pact.

In the plan they are putting on the table at this week's talks, the contras agree to disarm only if the Sandinista Army does the same.

The peace treaty signed by five Central American Presidents on Aug. 7 in Guatemala City, however, calls only on irregular or insurgent forces to disband. Government armies are left intact until later negotiations on the region's military balance.

The rebels are also demanding that the government dismantle the ``Sandinista Defense Committees,'' neighborhood organizations that are often called the eyes and ears of the revolution. Such a move would emasculate the Sandinistas' grass-roots party structure, and seems unlikely to occur.

Equally central to the Sandinistas' political program, and also targeted in the contra cease-fire proposal, are state farms and privately owned agricultural cooperatives whose members must serve in self-defense militia.

Those units are at the heart of the government's land reform project - a project the contras would roll back with their demands that state-owned land be divided up among individual peasant farmers and the armed co-ops be dismantled.

The Nicaraguan rebels are also calling for other measures such as generous wage increases, an end to compulsory military service in the Sandinista Army, and abolition of the ration cards that guarantee Nicaraguans minimal quantities of basic foodstuffs at subsidized prices.

These goals all have one thing in common: they are political demands. And if the Sandinista government has been firm on one point, it is that Managua will not talk politics with the contras unless they take the amnesty and join the civilian political process.

The Central American peace pact, the Sandinistas say, provides for political negotiations only in the ``National Dialogue'' among all disarmed political forces. As long as the contras keep their weapons, Managua says it will discuss with them nothing but the technical aspects of a cease-fire.

To stress the point, the Sandinistas have named Army intelligence chief Maj. Ricardo Wheelock as head of their negotiating team.

It is not yet clear how long this first round of negotiations will last. Since Major Wheelock has refused to meet the contras face to face: Mediator Miguel Cardinal Obando y Bravo will be shuttling between the two delegations transmitting their positions.

Cardinal Obando y Bravo, however, accepted the post of mediator only on the condition that he play a more active role than that of messenger.

The Cardinal will need to bring all his powers of persuasion to bear if he is to push the two sides onto some common ground.