The tug-of-war over a 6-year-old Cuban boy who survived a disastrous boat trip to Florida should be settled by "what would be best for the child," President Clinton said yesterday. But an influential Cuban American organization said the boy should remain with relatives in Florida and warned the administration against "playing into [Cuban leader Fidel] Castro's hands."

In Havana, thousands of people--including many students in their school uniforms--demonstrated for the fourth straight day in front of the building that houses the U.S. diplomatic interests section along the city's oceanfront boulevard, the Malecon.

The boy, Elian Gonzalez, has literally become a poster child for the politically charged issue of U.S.-Cuban relations since he was found Nov. 25 clinging to an inner tube off the Florida coast. His mother and stepfather had died after a powerboat loaded with 14 people sank during an attempt to reach the United States.

In Miami, the Cuban American National Foundation has printed posters of Elian lying on a stretcher, depicting him as a victim of communist repression. But in Havana, his picture has been plastered on one of two large billboards opposite the U.S. interests section, with the slogan "Return Elian to his country." The other billboard has a picture of Elian's empty school desk and the caption, "Send Elian back to his classroom."

Since his rescue, the boy has been staying with his father's uncle and cousins--one of whom arrived from Cuba just four months ago--pending a Dec. 23 hearing of the Immigration and Naturalization Service (INS).

Faced with the street demonstrations in Havana and demands from Cuban American groups that the boy be allowed to stay in Florida, Clinton tried to keep out of the fray.

"The question is--and I think the most important thing is--what would be best for the child. And there is a legal process for determining that," he said at a White House news conference. "I don't think that politics or threats should have anything to do with it, and if I have my way, it won't."

The Cuban American National Foundation, a strongly anti-Castro organization, said the United States should insist that Cuba allow the boy's father, his sole surviving parent, to travel to Florida to make a decision free from political pressure.

"We have said from the beginning that the only hostage here is the boy's father, who is not being allowed by the Cuban government to come to the United States and make a decision about whether the boy stays or goes, without any pressure from the Cuban government," said Ninoska Perez, a spokeswoman for the group.

In Havana, Castro said last night that the father of the boy had told him that he was not interested in traveling to the United States or in speaking with a U.S. government representative in Cuba unless it was to "communicate the day, hour and means" of the child's return.

In his most extensive comments since the boy was rescued, Castro said, in a statement read by a student leader at last night's demonstration in the Cuban capital, that he has "no desire to humiliate the United States" and was not issuing an ultimatum. But, he said, Cuba's "irritation and indignation" would not be assuaged until the child is returned.

Cuba has charged that the U.S. failure to return Elian to his father violates an accord signed in 1994 to halt illegal migration to the United States, and the government in Havana has vowed to keep demonstrations going until the boy is repatriated. Yesterday, the protest featured salsa music, a popular singer of children's songs, dancing, speeches and people holding signs saying "We love you, Elian" and "We're waiting for you, Elian."

Formally, the Cuban government also has sent the United States a diplomatic note demanding Elian's return; the State Department said it will reply by today and promised to outline the father's rights and the procedures he can use to request his son's return.

The State Department said the INS will contact the boy's father, Juan Miguel Gonzalez, who works as a hotel doorman in Veradero, Cuba's main beach resort east of Havana. Spokesman James Foley added that if the father wants to go to Florida, the United States will issue him a visa, but it remains unclear whether the Cuban government would allow him to leave. U.S. legal experts said that the father also could agree to let others represent him in the United States.

If the INS rules that the boy should be returned to Cuba, relatives in Florida can challenge the INS determination in court.

"We should let the people who are responsible for this, who have a legal responsibility, try to do the right thing by the child," said Clinton. "These decisions are often difficult even in domestic situations, and--but I hope that is what will be done, and it should be done without regard to politics."

"It's a curious intersection of immigration and family law," said David A. Martin, a professor of law at the University of Virginia and former INS general counsel. Under a 1966 special immigration law, people who make it to U.S. shores from Cuba can receive permission for permanent residence after one year. But under family law, the father would usually get custody.

Though Clinton said it wasn't his decision, Martin said there is a precedent for high-level action: During the Reagan administration, then-Attorney General Edwin Meese issued a "departure control order" that enabled a minor--a 12-year-old Ukrainian--to remain in the United States against the will of his parents, who were returning to the Soviet Union. "I think this is one that should go to the family court," Martin said.

"It's very straightforward and simple," said Bernard Perlmutter, director of the Children and Youth Law Clinic at the University of Miami Law School. "The right of the child is to be raised by a parent." But, he noted, "this is a case that is extremely complex not so much because of the custodial question, but because of the political ramifications."

Staff writer Karen DeYoung contributed to this report from Havana.