Secretary of State George P. Shultz and Nicaraguan President Daniel Ortega will meet here early Saturday to discuss Ortega's proposals for improving relations between the United States and his leftist Sandinista government.

U.S. and Nicaraguan officials said the meeting, set for 7 a.m., was arranged in informal discussions this morning between Nicaraguan protocol officers and L. Craig Johnstone, deputy assistant secretary of state for inter-American affairs.

The meeting had its genesis in Ortega's response last night to the verbal offensive launched by the Reagan administration last week against the Sandinistas. It began when President Reagan told a news conference he intended to make the Sandinistas cry "uncle," and Shultz subsequently renewed calls for Congress to approve a new program of covert aid for Nicaraguan rebels, known as contras, fighting the Sandinistas.

Ortega said his government planned to send 100 Cuban military advisers home and also would impose a moratorium on the acquisition of new weapons systems as part of a series of steps intended to renew peace talks within Central America and with the United States.

Ortega also said that since he and Shultz would both be here to attend today's inauguration of Uruguayan President Julio Sanguinetti, he hoped that the two could meet.

En route here yesterday, Shultz told reporters aboard his plane that he was willing to see Ortega, whom he met in Managua last June 1, and "listen carefully" to his views.

The U.S. and Nicaraguan parties are housed two floors apart in Montevideo's Victoria Plaza Hotel. U.S. officials said initially that they could not proceed until Shultz had a formal request from the Nicaraguans.

"This morning, two Nicaraguan protocol officers came from the third floor up to the American delegation on the fifth floor, talked with Johnstone, and the meeting was set up," a U.S. official said.

However, U.S. officials accompanying Shultz stressed that the secretary does not intend the meeting to be a negotiating session leading to resumption of the bilateral talks that were being conducted by Nicaraguan Deputy Foreign Minister Victor Hugo Tinoco and U.S. Special Ambassador Harry W. Shlaudeman in Manzanillo, Mexico.

The United States has suspended participation in the Manzanillo talks because U.S. officials contend that Nicaragua was using them in hopes of making a separate deal with the United States that would bypass the multilateral talks, known as the Contadora process, seeking a comprehensive peace plan for Central America.

The official said Shultz will stress to Ortega that the United States still regards Contadora as the principal forum for resolving the region's conflicts. They said he also will restate the four points that the United States regards as crucial for any settlement.

They are Nicaragua's agreement to halt aid to insurgent movements in neighboring countries, severing of military ties with Cuba and the Soviet Union, reduction of the Nicaraguan armed forces to a size that will not threaten its neighbors and meeting the original goals of the 1979 revolution including political pluralism.

The officials said that the administration regards Ortega's proposals as a propaganda ploy and added that, while Shultz will keep "an open mind," the United States does not expect much progress to result from the meeting Saturday.

Shultz is expected to elaborate on this position at a news conference before his departure Saturday. Ortega also has scheduled a news conference here later in the day.

In another sign of the administration's concern with Central America, Shultz met here early today with Costa Rican President Luis Alberto Monge. Tonight he had dinner with the delegation heads of the four Central American countries allied in varying degrees with the United States: El Salvador, Honduras, Guatemalaand and Costra Rica.