After years of controversy, the U.S. Navy today began what it says will be its last firing exercise on this embattled island. But bitterness remains on both sides of the six-decade relationship the Navy has had with this town's 10,000 residents.

Last week, the Navy said it would expand operations on several mainland bases and give up use of this island as a bombing range. But today, demonstrations continued with some protesters sneaking onto the 12,000-acre facility. At least five were detained by authorities.

"The Navy has lied to this town so many times over the years, nobody believes them," said Nilda Medina, an organizer speaking from the string of protest camps set up in front of the Navy's Camp Garcia military reservation. "We always said, as long as they keep bombing, we'll keep engaging in civil disobedience."

President Bush has ordered an end to the bombing exercises here by May 1. The unhappiness of U.S. military leaders over the controversy has been just as evident as the protesters' anger.

"I acknowledge the situation with regard to Vieques with extreme disappointment -- our sailors and Marines deserve better," said Marine Corps Commandant Gen. James Jones in a memo to Secretary of the Navy Gordon England, part of a certification to the White House and Congress that the Navy had found alternatives to Vieques.

"Some in Puerto Rico (particularly in Vieques) have demonstrated an appalling hostility towards sailors, Marines and their requirement for pre-deployment training; this at a particularly dangerous time in our nation's history," Jones said.

But Vieques residents say they have shouldered more than their fair share of the national defense burden since the Navy took over three-quarters of their island in the early 1940s.

"I know they don't want to leave, but the big losers here have been the Viequenses," said 69-year-old Radames Tirado, a former mayor whose childhood home was expropriated by the Navy and knocked down by bulldozers. "We have been fighting for 60 years to get back the lands they took from us."

The hard feelings between the uneasy neighbors, forged by years of what residents said were broken Navy promises for economic development and other assistance, is one reason why many who live here say the protests will continue.

The current month-long exercise is for the USS Theodore Roosevelt Battle Group, comprising nine ships, two submarines, fighter jets and about 8,000 military personnel.

Protests have become a staple activity here since an April 1999 training accident killed a civilian security guard, David Sanes Rodriguez, turning years of resentment against the Navy into calls for a halt to its bombing. The issue has been a rare point of unity among Puerto Rico's commonwealth, statehood and independence supporters.

Hundreds of Puerto Ricans, as well as U.S. supporters, including environmental attorney Robert Kennedy Jr., actor Edward James Olmos and Al Sharpton, have been arrested during demonstrations accompanying the various war games that have taken place since then.

While many here are celebrating the end of bombing, some say another battle will be waged to press the federal government to clean up and turn over the vast swaths of land it still owns in the east and west ends of the island. Most of the land is slated to be transferred to the Department of the Interior to become a wildlife reserve.

The cleanup issue is of particular concern to many here, who suspect that contaminants from Navy bombing could be harming the environment and health of residents, who suffer from a cancer rate about 26 percent higher than that of the main island of Puerto Rico.

Those concerns increased after recent revelations that a Navy destroyer sunk about 900 feet off the Vieques shore was used as a target ship for nuclear tests in the Pacific in 1958 and Pentagon acknowledgement that chemical weapons simulants were tested on the island in the 1960s.

Studies by University of Puerto Rico scientists and others have turned up contamination in local plants, groundwater and seafood, but a series of reviews by the federal Agency for Toxic Substances and Disease Registry have stated that the toxins are not in sufficient quantities to pose a health risk to local residents.

The Navy has repeatedly denied that its activities harm the environment or the health of residents.