Mexican Foreign Minister Jorge Castaneda will travel to Cuba and Nicaragua this weekend to convey U.S. proposals aimed at finding political solutions for the growing confrontation throughout Central America, Foreign Ministry officials said today.

The trip will be an unexpectedly rapid followup to last Sunday's talks between Secretary of State Alexander M. Haig Jr. and Castaneda in which the United States agreed that Mexico act as a go-between with Nicaragua and Cuba.

Haig and Castaneda have already conferred twice this month to discuss a broad peace initiative proposed by Mexican President Jose Lopez Portillo on Feb. 21.

According to the Foreign Ministry, Castaneda has requested a meeting with Cuban President Fidel Castro in Havana for Saturday and has asked to see on Sunday three top members of the Nicaraguan government, junta members Sergio Ramirez and Daniel Ortega, and Jaime Wheelock, minister of agriculture and member of the Sandinista high command.

The officials declined to say what specific proposals Castaneda would carry to Havana, which is described by Washington as the pivot of the region's troubles. "He will inform of his conversations with Haig in New York and convey U.S. proposals and some of our own ideas. We can't say anything more," an aide to Castaneda said.

As Haig characterized the talks with Castaneda after their meeting Monday, the United States would pursue a nonaggression pact with Nicaragua and clamp down on anti-Sandinista exiles in the United States if Nicaragua would forswear any aid to guerrillas in El Salvador. Import of heavy weapons would be restricted in the region.

The Mexican foreign minister, informed sources here said, is expected to propose direct meetings between U.S. and Cuban officials on the one hand and U.S. and Nicaraguan officials on the other. The Mexican plan has called for such talks from the outset.

Last November, Mexico arranged a secret meeting between Haig and Cuban Vice President Carlos Rafael Rodriguez in Mexico City. Afterwards, the meeting was described by one official here as "not very productive, but an achievement in itself." Since then, Mexico has insisted there should be a followup to the talk.

The Lopez Portillo government has been increasingly worried about the escalation of violence, the polarization between the opposing sides and the potential for U.S. intervention in the region, which it says threatens Mexico's own stability.

Castaneda returned to Mexico late yesterday from New York, where he attended a series of talks with U.S. and United Nations officials. Early this morning he met with Lopez Portillo to work out the next step to be taken, given the "encouraging" U.S. response.

Foreign Ministry sources said that in New York, Castaneda had turned down a Cuban request that he meet with Raul Roa, Cuba's ambassador to the United Nations. But he had briefly seen Nicaraguan Wheelock, member of the nine-man Sandinista national directorate. They had no in-depth talks, the sources said, but at Wheelock's request Castaneda had provided a vague outline of U.S. proposals and plans, mainly to assuage Nicaraguan fears of imminent U.S. aggression.

The positive reaction to Mexico's diplomatic efforts in the U.S. Congress and press and the international attention it has received have put officials here in an upbeat mood.

Some officials commented somewhat icily on what they regarded as Haig's snide remark in New York Monday that the United States had not authorized Mexico to negotiate with Cuba or Nicaragua in its behalf.

"We realize that Haig wanted to cut back the Mexican role, but we never intended to be in the arena as one of the players," said one government official, "as long as we achieve our objective to get political negotiations going between the different sides. Lopez Portillo offered Mexico as a communicator."

Asked how Mexico perceived a U.S. commitment to follow through with broad political negotiations, including a series of nonaggression pacts, one key government official replied, "The U.S. is trying to show flexibility but it is still playing with two hands. With one hand it begins negotiations, with the other hand it is applying covert action. But we remain very optimistic."