Cubas President Fidel Castro flew into Kennedy Airport early this morning on his first visit to the United States in 20 years.

Castro, whose entourage was thought to number about 200, was protected by a security cordon of thousands of police and Secret Service agents.

He was taken to the Manhattan headquarters of the Cuban mission to the United Nations where he will make final preparations for his address to the U.N. General Assembly on Friday.

Yesterday, a U.N. spokesman said that Secretary General Kurt Waldhein will welcome Castro at his office at 10:30 Friday. Their discussions will be followed by a brief meeting with the president of the General Assembly.

At 11:30 a.m. Castro is to begin his address. He is expected to repeat the harshly anti-U.S. speech with which he opened the summit of nonaligned nations in Havana last month. There has been no indication whether Castro will address the issue of Soviet troops in Cuba, which President Carter declared "answered" in his press conference Tuesday.

Castro is coming here as chairman of the 94-nation nonaligned movement, and his speech is intended to report on the movement's position on various world issues, including the Middle East, Cambodia and Southern Africa.

Castro also is expected to deliver a separate address to the non-aligned nations Friday afternoon. The organization ended the Havana summit sharply divided over Cuba's leadership, amid charges that Castro was trying to make the movement more militant and draw it closer to the Soviet Union.

Castro's oponents within the movement already have attempted to water down some of the more outspoken positions taken by the summit, and in some cases have succeeded. A number of nonaligned nations voted against the Cuban position and ended up on the winning side of a U.N. vote late last month prohibiting the Vietnamese-backed Cambodian government of Heng Samrin from taking over the U.N. seat held by the Pol Pot government he ousted.

According to the United Nations, Castro will hold no press conference during his visit here. Although the State Department said today there are no restrictions on where he may travel, it is unlikely he will leave New York.

Last Friday, when it was first rumored that Castro would make the trip, more than 3,000 noisy anti-castro demonstrators gathered outside the United Nations. Many more are expected this week, despite police plans to close off streets around the U.N. building while Castro is inside.