PANAMA CITY, Panama (AP) _ Thirteen Latin American foreign ministers meet here for another round of talks toward a Central American peace treaty Friday, the date they were supposed to sign a final document, the Panamanian government said.

But Costa Rica's foreign minister, Rodrigo Madrigal Nieto, said he was not sure he would attend because of what he described as confusion about who would be at the meeting.

''Confusion exists about the participation of the Central American foreign ministers at the meeting called by the Contadora group for tomorrow, the day set for the signing of a peace agreement,'' Madrigal Nieto told The Associated Press in an interview in San Jose, the Costa Rican capital.

A Panamanian Foreign Ministry communique said the 48-hour meeting was called ''to officially conclude negotiations'' on the peace treaty ''and proceed to formalize this international instrument.''

The communique did not specify what it meant by ''formalize'' and did not specify a date for signing a Contadora treaty.

Mexico, Venezuela, Colombia and Panama formed the Contadora group in January 1983, taking the name from the Panamanian resort island where their foreign ministers first met.

The group earlier this year set June 6 as the target date for signing an agreement for peace in Central America. The general framework of the negotiations had concentrated on demilitarization of the region, the withdrawal of all foreign military advisers and an end to foreign military maneuvers in the area.

But at a meeting in Guatemala May 24-25, five Central American presidents called for further negotiations beyond the deadline if no agreement was reached.

In a joint communique, the presidents of Guatemala, El Salvador, Costa Rica, Nicaragua and Honduras said the efforts to reach a negotiated peace in Central America should not be ended by the deadline.

So far, there has been no agreement on vital issues involving implementation and verification of the peace agreement.

Also meeting with the representatives of Contadora and Central America here are the foreign ministers from Peru, Uruguay, Argentina and Brazil, who formed a support group last year intended to help the talks produce positive results.