Mexican Foreign Secretary Bernardo Sepulveda, commenting on two days of meetings here with U.S. Secretary of State George P. Shultz, criticized the United States today for refusing to resume talks with Nicaragua's leftist government.

Shultz, who departed this morning with a high-ranking U.S. delegation, reaffirmed the U.S. position that such talks will remain suspended until the Sandinista government agrees to meet with representatives of Nicaraguan antigovernment guerrillas.

The dispute over Central America, which had been expected, was the only significant point of public disagreement following the talks on a wide range of subjects. Shultz called the meetings "fruitful," while Sepulveda said that they were "very successful from all points of view."

The two countries agreed to begin meetings in September to explore the possibility of negotiating a "framework agreement," or set of procedures, for resolving trade and investment disputes. Mexico also agreed to establish new immigration and customs posts at four bridges over the Rio Grande.

In the first official U.S. statement on widely reported voting irregularities in Mexico's July 7 elections, Shultz said that "these are matters for the people of the country to discuss." The U.S. Embassy here carefully has avoided making any comment on the allegations.

Sepulveda said that the U.S. refusal to talk with the Sandinistas was hurting peace efforts in Central America. Washington suspended direct talks with Nicaragua, which were hosted by Mexico, in January.

"We think that the cancellation, or suspension, of these conversations is not useful. It does not help the Contadora process," Sepulveda told a news conference shortly after seeing off Shultz at the airport.

Mexico is one of four members of the Contadora group, which has been trying for more than two years to hammer out a regional peace package. The group, which also includes Venezuela, Colombia and Panama, issued a formal call Monday for the United States to resume talks with Nicaragua.