By FENTON WHEELER

HAVANA - Two captured anti-Castro commandos told a news conference Sunday they carried bullets tipped with potassium cyanide in a plot to kill Prime Minister Fidel Castro.

The two were among six captured Cuban exiles the Cuban government put on display at an extraordinary news conference lasting more than three hours. All six said they were recruited and trained by the U.S. Central Intelligence Agency in Florida.

Details of the plot against Castro were not given. But two of the captives said assassination of Castro was part of their mission. Bullets coated with the deadly poison were among the captured arms, Cuban authorities said.

The carefully elicited admissions were made before delegates to the Havana conference of revolutionaries from 27 Latin-American countries and visiting U.S. newsmen. The performance obviously added spice to the meeting of the Latin American Organization of Solidarity (OLAS).

It also apparently was aimed at offsetting Venezuelan charges that Cubans landed guerrillas near Caracas, Venezuela, in May.

The Communist party newspaper Granma called the prisoners' admissions "proof of the crimes that imperialism makes against Cuba."

Under questioning by three Cuban army officers, two of the exiles said they were agents of the CIA. In addition, four men captured July 18 were displayed with the arms and explosives the Cubans said they carried for terror and sabotage.

Cuban authorities said they also had arrested a fifth man, identified as Placeo Hernandez. They said he was shot and wounded while resisting arrest and he was not at the news conference.

In Miami the militant anti-Castro exile group, Second Front of Escambray, said the men captured in Cuba were guerrillas from their organization.

Andres Nazario, secretary general of the Second Front, said the expedition left for Cuba nearly four weeks ago.

"They were going to infiltrate Cuba on a mission of subversion and guerrilla warfare and were going to join up with patriots inside Cuba," Nazario said.

The military commander of the Second Front group, Eloy Gutierrez Menoyo, was captured in Cuba two years ago after infiltrating on a similar mission. He was succeeded as commander in Miami by Armando Fleites.

The six prisoners were said to have lived in Miami but to have operated out of Tampa, Naples and Key West. All six said they were trained and recruited by the CIA.

Cuban authorities said the four men who brought arms to Cuba were captured July 18 near Honda Bay in westernmost Pinar del Rio Province. They were identified as Jose Roy Rodriguez, Alberto Laucerica Diaz, Francisco Avila Azcuy and Pablo Garcia Roqueta. They said they were members of the Second Front.

Cuban Army Lt. Jose Hamel identified one alleged CIA agent as Vincente P. Gonzalez Migoyo and said he was captured Saturday in Matanzas Province.

The other alleged CIA agent was identified as Jose Rabel Nunez, a Cuban government defector reported captured Sept. 4, 1965.

Fleites said in Miami that only four of the six men displayed in Havana were members of the Second Front team, which he said was commanded by Avila, He said he knew nothing about the other two men, Gonzalez and Rabel.

The exile commander said Avila lives in Miami but has no family here. The other men have families here, but Fleites said they were too upset to talk to newsmen.

Fleites said, "The objective of this mission most certainly was to kill Castro."

Fleites declined to comment further pending a news conference later in the week. A source in the Second Front said Fleites was under an agreement with Life magazine which the source said had helped finance the trip in exchange for exclusive rights to the story.

The prisoners appeared frightened at the outset of the conference but managed a few smiles during the more than three hours of questioning.

They said they did not know if they were going to be shot. Newsmen were permitted to question the six. Although their stories were confusing and conflicting at times, it soon became apparent that the two men alleged to be CIA agents were accused of different operations.

In the midst of the confessions, the government also played a tape recording from a man it identified as CIA agent Tony Cuesta, captured in May 1966.

The government said two of the men betrayed their comrades to Cuban authorities, but it did not identify the two.

Garcia denied that killing the Cuban prime minister was part of his mission, but Laucerica said one objective was "the physical elimination of the leader of the Cuban revolution, Fidel Castro."

Roy said he was paid $200 for the mission and told a lengthy story of CIA recruitment and training in "security house" in Miami. He described carrying out similar clandestine missions to Cuba before, but said the missions had been discovered and had not been able to land.

Under questioning by newsmen, Laucerica was asked if he felt his group could have carried out an assassination. He replied with a smile: "Circumstances for me to say no."

Cuban authorities said the four-man group came ashore from an "armed mother ship."