In a flurry of diplomatic activity here, Central American nations endorsed three new initiatives aimed at reviving the region's moribund peace process, officials said today.

Foreign ministers of the five Central American countries formally renewed the Contadora peace talks, lifting a suspension declared in December. They did so by backing a document that also urged the United States to resume direct negotiations with Nicaragua's Sandinista government.

In addition, the five countries agreed to consider forming a Central American regional legislature similar to the European Parliament.

Finally, all of the Central American nations except Costa Rica agreed to hold a regional summit in Guatemala in the spring. It was expected that Costa Rica also would participate.

Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica remained at odds on a number of issues that stalled the three-year-old Contadora negotiations. Some diplomats predicted that renewed momentum in the peace talks would make it more difficult for the U.S. administration to persuade Congress to approve military aid for the Nicaraguan rebels.

"The problem is that the United States and Contadora are going in diametrically opposed directions. It's going to make it harder for the Yanks," said a senior diplomat of a U.S ally here.

A major factor contributing to an upbeat atmosphere here was the active role of Guatemala's new president, Vinicio Cerezo. He proposed both the Central American legislature and the regional summit. The diplomatic activity took place while dignitaries were here to attend Cerezo's inauguration yesterday as this country's first civilian president since 1970.

Another factor was pressure from four South American democracies -- Argentina, Peru, Brazil and Uruguay -- that began last summer to participate directly in the Central American negotiating process. They comprise what is called the Support Group for the Contadora nations: Mexico, Venezuela, Colombia and Panama.

The Contadora Group, named for the Panamanian island where it first met in January 1983, has been seeking to put together a package deal to achieve a negotiated end to Central America's conflicts.

Under a regionwide treaty drafted last autumn, all five Central American countries would be obliged to trim their arms stockpiles, send home foreign military advisers, halt support for guerrillas fighting in neighboring countries and guarantee a democratic political process at home.

But the Contadora effort has been stymied by differences between Nicaragua on the one side and U.S. allies El Salvador, Honduras and Costa Rica on the other.

On Nov. 21, the Central American countries failed to meet a self-imposed deadline for signing the draft treaty. In early December they agreed to suspend talks until May, when new presidents would be in place in Guatemala, Honduras and Costa Rica.

Worried that the peace process might die altogether, the Contadora countries and the Support Group met last weekend in Caraballeda, Venezuela, and approved a 10-page statement aimed at resuming the talks. It called on Washington to resume direct talks with Nicaragua that were suspended a year ago.

Late last night, foreign ministers of the five Central American countries issued a two-page declaration that endorsed the Caraballeda document. "It means that we are going to reactivate the talks regarding the Contadora initiative," Honduran President-elect Jose Azcona said.

The Caraballeda document also said that the Central American countries would begin a "consultative process" with the goal of "constituting a parliament in the region."

This is a pet project of Cerezo's, but a dispute already has broken out over whether members should be selected directly in new elections or should be chosen from existing national legislatures. Nicaragua was resisting direct election of representatives, diplomats said.

Agreement came this morning on the meeting of the five presidents at an unspecified date this spring. Cerezo is to be host.