In a change of plans as yet unexplained, it was announced yesterday that Cuban President Fidel Castro indeed plans to address the U.N. General Assembly in New York this week.

"We understand he will be coming in the middle of week," a State Department spokesman said after the Cuban government applied for a visa at the U.S. interests section of the Swiss Embassy in Havana.

Last week, the United Nations announced officially that Castro would not come but that Cuban Vice President Carlos Rafael Rodriguez would speak in his stead.

Castro is to address the assembly in his capacity as the new head of the nonaligned movement, according to a U.N. spokesman in New York yesterday.

A spokesman for the Cuban interests section of the Czechoslovak Embassy in Washington said it had not been informed of the change in plans. After the initial U.N. announcement last week, the Cubans had pointed out that only the Cuban government in Havana could state Castro's plans officially.

The United States and Cuba do not have diplomatic relations but operate interest sections through the Swiss and Czechoslovak embassies.

Castro has not visited the United States since the explosive 1960 U.N. General Assembly session.

The State Department spokesman said "we don't have a precise date yet" for Castro's arrival but he thought it would be in the middle of the week.

"There are no plans for a meeting between him and any U.S. officials," the spokesman added.