* Plebiscite will be the fourth held since 1967
* Voters to choose if they want a change in political status
SAN JUAN, Puerto Rico, Nov 4 (Reuters) - Puerto Ricans, long divided over the U.S. Caribbean territory's political status, head to the polls on Tuesday in a vote that will help determine whether the island seeks to become the 51st U.S. state.
Debate over the island's status has long dominated politics in Puerto Rico, where political parties are formed around the preference for statehood, independence or its current status as a self-governing commonwealth.
Puerto Ricans have voted to remain a U.S. territory in four previous votes held since 1967, but the margin of victory has decreased over the years.
The plebiscite was proposed by Republican Governor Luis Fortuno, president of the New Progressive Party, which supports statehood. It is alternately viewed by Puerto Ricans as an opportunity to improve the island's economic future, a chance to shake off the vestiges of its colonial past or a ploy by Fortuno to win a second term.
The vote coincides with gubernatorial and municipal elections.
Supporters of the current status describe it as a bilateral pact that allows the island some autonomy while enjoying being a part of the United States. But critics say it means Puerto Rico is in effect a colony under the complete authority of the U.S. Congress.
Under its current commonwealth status, Puerto Ricans living on the island are U.S. citizens but they cannot vote in presidential elections and their only representation in Congress is a non-voting member of the U.S. House of Representatives.
Most Puerto Ricans pay no federal income tax, but they contribute to the Social Security retirement program, are eligible to receive federal welfare benefits and have long served in the armed forces.
Some statehood supporters like Ingrid Reyes, a 41-year-old unemployed personnel manager, argue the status issue has been a lengthy distraction for the island, diverting attention from more pressing issues like a stagnant economy and a stubborn unemployment rate of 13.6 percent.
"Until status is resolved, we won't be able to focus on the real issues," said Reyes. "Nothing has changed for the last decade, and keeping with the status quo won't improve things."
Voters will be asked two questions in the plebiscite about the political status of Puerto Rico, an island of nearly 4 million people.
The first, a yes-or-no question, asks if voters agree that Puerto Rico should continue with its current status.
The second calls on voters, regardless of their answer to the first question, to choose their preference among three non-territorial options - U.S. statehood, independence or sovereign free association with ties to the United States.
A poll conducted two weeks ago by the ASISA Research Group showed 48 percent favored statehood, 41 percent wanted sovereign free association and 6 percent backed independence. The margin of error was plus or minus 3 percentage points.
Any change in Puerto Rico's status would ultimately have to be approved by the U.S. Congress.
Senator Alejandro Garcia Padilla, the president of the Popular Democratic Party, or PDP, which favors keeping Puerto Rico's current status, has criticized the vote as an attempt by Fortuno to boost voter turnout and possibly his chances for re-election.
Garcia Padilla is challenging Fortuno for the job of governor.
Some in the PDP have called for an "improved commonwealth" status that would grant the island more autonomy over its affairs while maintaining a "permanent" relationship with the United States, which would continue to guarantee U.S. citizenship for Puerto Rico's residents.
Critics say such an arrangement is not possible under the U.S. Constitution.
Other prominent PDP members back sovereign free association, where the terms of the relationship between a sovereign Puerto Rico and the United States would be detailed in a new pact.
Garcia Padilla has equated free association with independence and is calling on PDP supporters to vote "yes" on the first question to maintain the political status quo, while leaving the second part of the ballot blank.
Other prominent PDP members, however, are openly supporting the sovereign free association, which is defined on the ballot as a "free and voluntary political association, the specific terms of which shall be agreed upon between the United States and Puerto Rico."
Marcos Mirabal, a 44-year-old psychologist, said he will likely vote for free association.
"My preference is we have as many powers as possible to run our own show but without avoiding the reality of our political and historic relationship with the U.S.," he said.
In 1998, the last time voters were asked to choose their status preference, just over 50 percent chose a "none of the above" option that was backed by the pro-commonwealth PDP.
The party opted not to support a "commonwealth option" on the ballot because it was defined as a territorial status subject to congressional authority.
The United States seized Puerto Rico as war booty from Spain following the Spanish-American War in 1898. The island was granted a larger degree of autonomous rule under commonwealth status in 1952.