VIEQUES, Puerto Rico - With helicopters swooping overhead, 2,000 U.S. troops staged an amphibious practice invasion of this contested Puerto Rican island on Tuesday - despite claims that some activists protesting the huge NATO exercise had broken into the training ground.
Hovercraft roared onto Vieques island's Red Beach, disgorging troops and vehicles that disappeared into a pine forest in an operation lasting 20 minutes.
The two-week exercises, which began Monday, simulate a NATO-led U.N. peacekeeping operation dubbed ''Unified Spirit.'' They include 50 vessels, 31,000 U.S. soldiers and an unspecified number of troops from Canada, France, Denmark, Germany and Britain.
''This exercise is critical for putting all those people together,'' Marine commander Col. Paul Lefebvre said after the landing by troops from the USS Nassau, USS Nashville and USS Portland.
Lefebvre complained of the ban on using live ammunition during the exercise.
''The goal is to fire as much as we can to gain as much proficiency as we can,'' he said. ''That's the stress, that's the reality of real combat.''
The restriction on live fire is part of a 10-month-old directive by President Clinton to calm mounting Puerto Rican opposition to the military's use of Vieques, where 9,400 people live. The directive also limits training to 90 days a year.
The Navy expropriated two-thirds of the 20-by-4-mile island for exercises in the 1940s. It says troops have trained here for every major conflict since World War II.
Resentment became widespread after a U.S. Marine Corps jet mistakenly dropped two 500-pound bombs off target in April 1999, killing a civilian guard on the range. Protesters invaded the training ground and thwarted exercises for more than a year until U.S. Marshals forcibly removed them in May.
Earlier Tuesday, Vieques activist Ismael Guadalupe said an unspecified number of people again entered restricted Navy land Monday night hoping to disrupt exercises. But there was no sign of the protesters during the landing, and the Navy said it detained no trespassers.
Organizers said the protesters had entered near the bombing range on Vieques' eastern end and had supplies for three days - long enough to disrupt planned exercises that include firing dummy shells from ships onto the bombing range.
Navy opponents say such exercises over six decades have stunted economic growth, scared away tourism and - despite a dispute over medical evidence - endangered the health of residents.
The Navy says the Vieques training is vital to national defense and that the island is uniquely suited because of its topography, location near wide expanses of open sea and the nearby deep-water port in Puerto Rico.
Still, on Tuesday the White House confirmed the government was looking at other sites because of a promise by Clinton that the Navy will leave Vieques by 2003 if islanders vote against it in a referendum.
Jeffrey Farrow, Clinton's adviser on Puerto Rico, said the owners of San Jose - an uninhabited, 12,000-acre island 55 miles south of Panama City - had offered to sell the land to the Navy.
''The Navy is exploring what the options are for Vieques,'' Farrow said. ''The president is committed, the Navy is committed and the Congress is committed to the Navy leaving after this period if the people vote for it.''
A consultant brokering the sale, former Boca Raton Mayor Emil Danciu, said the island's two American and three Panamanian owners want $35 million - a lower sum than the Navy has agreed to invest in Vieques should the base be allowed to stay.