Honduran Foreign Minister Edgardo Paz Barnica said today that "a short and urgent period of negotiation" will be necessary to modify the proposed Contadora treaty in ways that would guarantee implementation and win approval by Central American nations.

Paz Barnica made his statement in an interview after he and three other Central American foreign ministers met to discuss the draft of the proposed "Contadora Act for Peace and Cooperation in Central America" with Secretary of State George P. Shultz.

The other ministers were from Costa Rica, El Salvador and Guatemala.

Shultz later told Latin American diplomats at a luncheon that amendments will be needed "to make this treaty into something that will really work."

Neither Shultz nor Paz Barnica spelled out what process could be followed to make the proposed treaty more precise. Paz Barnica indicated, though, that negotiations involving all five Central American countries, including Nicaragua, would be necessary after the Oct. 15 deadline for comments by nations involved.

Nicaragua's surprise announcement two weeks ago that it would sign the treaty as written brought greatly increased international attention to the Contadora process, named for a Panamanian island where it was inaugurated. It also brought to the surface pressing concerns and second thoughts by the United States and its regional allies.

Paz Barnica expressed doubt that Nicaragua would agree in forthcoming negotiations to nail down such key questions as the makeup and powers of a verification commission and the precise timing of demilitarization actions called for in the treaty.

"Nicaragua expressed its willingness to sign for propaganda ends," Paz Barnica said. He added that Nicaraguan refusal to make changes would be an indication of insincerity and that he sees no sign of Nicaraguan willingness to comply with restrictions contained in the document.

According to the State Department account of Shultz's meeting with the four Central American ministers, Shultz said: "It is important to complete the treaty-drafting job in a way that will work. Nobody wants to sign a treaty that won't work."

Shultz, meeting reporters Thursday, complained that under the current draft "there would be virtually a cessation of security assistance to, say, El Salvador whereas there wouldn't be a single Russian or Cuban military so-called adviser leave Nicaragua. And the period for negotiating that is set at 90 days with extensions of time expected . . . kind of an open-ended proposition."

As expressed to reporters and, in the U.S. account, to today's Central America meeting, Shultz also cited problems with details of verification.

A State Department spokesman said problems of staging and verification were related to the proposed arms freeze in Central American countries, withdrawal of foreign military advisers and ceilings on numbers of armed forces personnel.

Despite these difficulties, Shultz maintained that the United States continues to support the Contadora treaty and process and expressed optimism that changes can be made to the satisfaction of the non-communist countries.