David Efron was born in Cuba, moved to the U.S. territory of Puerto Rico when he was 8 and was naturalized a few years later, making him a full citizen of the United States.

His daughter Jennifer, 14, is a U.S. citizen by her birth in Puerto Rico. But the island's peculiar status makes her citizenship "statutory" and revocable by Congress, maintains Efron, a supporter of making Puerto Rico the 51st state.

Supporters of the current "commonwealth" arrangement deny that Puerto Ricans' citizenship is in any danger, and the issue has become a central one in the status referendum to be held Sunday.

During the past two years, Efron has poured tens of thousands of dollars into a lawsuit demanding that the U.S. government naturalize Jennifer -- seemingly redundant for someone who is already a citizen.

"I want my daughter to have a first-class, non-revocable type of citizenship," said Efron, a lawyer and real estate developer who divides his time between San Juan and Miami, where his family has lived for 12 years.

But his real goal is to get the U.S. court system to formally rule that the citizenship of Puerto Ricans is indeed revocable under commonwealth.

The issue dates to the 1917 Jones Act, when Congress unilaterally declared that Puerto Ricans "shall be deemed and held to be citizens of the United States."

That citizenship was kept when Puerto Rico became a "commonwealth" in 1952. So Puerto Ricans can travel, live and work in the mainland freely, even while enjoying trappings of nationhood such as their own Olympic team.

In the current campaign, statehood supporters have tried to sell the change, which many here fear would erode the island's Hispanic culture, as the only guarantor of citizenship.

Ivan Ortiz, local spokesman for the U.S. Immigration and Naturalization Service, would say only that "as far as the INS is concerned, a person born in Puerto Rico is a U.S. citizen."

But in a recent article, former attorney general Richard Thornburgh said he agreed that Puerto Ricans' citizenship is "granted by statute and not fully protected by the U.S. Constitution."

So far, the Supreme Court has not considered any case that would clarify the issue.

Congress has never moved to revoke Puerto Ricans' citizenship. But outgoing House Speaker Newt Gingrich (R-Ga.) and others have said recently that commonwealth is not permanently acceptable, suggesting that Puerto Rico should eventually choose between statehood and independence.

In a non-binding 1993 vote, islanders narrowly preferred keeping commonwealth.

Sunday's vote is again non-binding, but President Clinton has said he hopes Congress will abide by the result.

The choice this time is between statehood, commonwealth, independence and a fourth option called "free association," which is essentially independence with treaty ties.

The commonwealth movement has called on supporters to vote for "none of the above," to protest the wording of the commonwealth definition that suggests the citizenship can be revoked.

In Jennifer's case, the U.S. District Court in Southern Florida rejected the naturalization petition, arguing there was insufficient immediate danger that she would lose her rights.

The decision, however, said: "The court notes that Congress, if it does choose to revoke the statutory' United States citizenship of Puerto Ricans, may nevertheless make provisions for the naturalization of persons, like Efron, who were granted statutory' United States citizenship."

Efron said that wording constitutes agreement that Congress can revoke the citizenship of the 3.8 million Puerto Ricans on the island at some future date. Theoretically, it could also affect those among the 2 million Puerto Ricans living on the mainland who were born on the island.

"Puerto Ricans treasure their U.S. citizenship, but I don't think they realize how fragile their citizenship is," Efron said.