Two top officials of the influential Cuban American National Foundation are expected to be indicted next week by a U.S. grand jury in Puerto Rico in a plot to kill Cuban leader Fidel Castro during a trip to Venezuela's Margarita Island, their attorneys said Thursday.

The indictment against foundation president Francisco ``Pepe'' Hernandez and director Jose Antonio ``Toñin'' Llama is expected to be issued Tuesday. It caps a vigorous investigation that began 10 months ago when the U.S. Coast Guard stopped a boat carrying weapons, ammunition and military supplies off Puerto Rico.

One of the four Cuban exiles aboard the 46-foot vessel La Esperanza allegedly blurted out that they were en route to Margarita to carry out a plot to assassinate Castro, who would be participating in the Ibero-American Summit.

Since the October incident, investigators have found that Llama owned the boat and that one of the two .50-caliber sniper rifles belonged to Hernandez.

Tuesday's superseding indictment will add four defendants and at least one additional count to the four Cuban exiles already accused in the case, according to a court document.

A third foundation member, Alfredo Otero, is also expected to be charged. The identity of the fourth person to be indicted could not be confirmed and the precise charges against the foundation members were not immediately known.

Lawyers for Hernandez and Llama denounced the proceedings as ``politically motivated.''

``We feel and fear that there are political reasons behind this action,'' attorney Jose Quiñon said. ``We see . . . that the administration may be trying to come together with Cuba. Somebody is going to be sacrificed, and hopefully, it won't be Mr. Hernandez.''

Quiñon and attorney Manny Vazquez said U.S. prosecutors in Puerto Rico have ``a very weak case.'' They acknowledged that Hernandez owns the rifle and Llama owns the boat, but said there was no evidence linking their ownership to the alleged plot to kill Castro.

``Ownership of a rifle or a boat does not make you guilty of a crime,'' Quiñon said. ``The government has known this for years about the rifle and boat ownership.''

Hernandez and Llama did not comment during the packed press conference held at Quiñon's office at noon Thursday.

Powerful organization

Their lawyers said the prosecution of the case was aimed at weakening the powerful anti-Castro exile organization. The group, widely considered the most effective anti-Castro lobby, enjoyed unprecedented access to the White House during the Reagan and Bush administrations. The Clinton administration, the attorneys said, is making overtures toward Castro and considering softening the U.S. embargo, which the foundation supports.

``We have also noticed,'' Vazquez said, ``that since the chairman of the Cuban American National Foundation, Mr. Jorge Mas Canosa, died in November, efforts to bring down the Cuban American National Foundation have intensified.

``The enemies of the embargo are behind this action,'' he added. ``When Castro snaps his fingers, our government jumps.''

Clinton administration officials could not be reached for comment late Thursday.

Last November, Hernandez and Llama were subpoenaed to testify before the federal grand jury in San Juan investigating the alleged plot. Otero, the third foundation member implicated in the case, is a 62-year-old retired Miami businessman. His lawyer, Wilfredo A. Ruiz, said Otero is accused of being involved in ``communications'' in the plot. Last week, he took the Fifth Amendment when asked to testify before the grand jury, Ruiz said.

Aboard the vessel

Also accused in the case are four Cuban exiles who were aboard the vessel: Angel Alfonso, 57, manager of a textile firm in Union City, N.J.; Angel M. Hernandez Rojo, 64, a Miami lumber dealer; Juan Bautista Marquez, 61, a former Miami merchant seaman; and Francisco Cordova, 50, a commercial fisherman who lives in Marathon. They are accused of importing illegal weapons to the United States and giving false statements because, when first questioned, they denied the boat was carrying weapons.

By far, Francisco Hernandez, 61, is the most prominent exile among those allegedly involved in the plot.

A successful businessman who owned an agricultural firm with operations stretching from the Dominican Republic to Kenya, he has been the second most visible foundation figure, after the late Mas Canosa. As CANF's president and top executive officer, Hernandez devotes most of his time to the anti-Castro lobby.

The role of others in the case remains unclear.

The owner of the second rifle confiscated, Miami exile Evelio Pou, a veteran of the Bay of Pigs invasion, was questioned by the FBI, but he has not been named among those likely to be indicted.

Mixed reactions

Reaction in South Florida to the imminent indictments was mixed.

Roberto Rodriguez Aragon, president of the Cuban Patriotic Council, called Hernandez and Llama ``patriots.''

``It's absurd that the country that is supposed to be our ally against Castro's communism would prosecute people who want to liberate Cuba or who supposedly want to attempt to kill Fidel Castro,'' Rodriguez Aragon said. ``I wish they had been successful, if that was their purpose. There are 10 million people who have the same goal, only they don't have the means to do it.''

Others refrained from comment.

``I don't want to involve myself with anything that has to do with terrorism,'' said Eloy Gutierrez Menoyo, once a militant exile who now advocates peaceful change in Cuba and heads the group Cambio Cubano. ``I'm not a judge to evaluate [the indictments].''

Castro himself has publicly commented on the case.

According to the daily Granma, in a speech delivered July 26 in Santiago de Cuba, Castro said: `` Let's see how they can deny it. Let's see how they can deny that the boat that was going to commit the attempt at Margarita -- captured by pure chance after sailing from Miami to Puerto Rico -- belongs to the foundation and that the weapons belong to the foundation. Let's see how they handle that problem.''