After a brief delay because of overcast skies, Navy ships and fighter jets began pelting a firing range on this Puerto Rican island with inert bombs and shells in bitterly protested military maneuvers scheduled to end Tuesday. 

Thirteen more people were detained overnight for trespassing on federal land, the Navy said. Only a dozen stood outside the Navy's base Tuesday morning with flags and posters demanding "Peace for Vieques." 

The latest round of maneuvers would end by nightfall and the ships and jets will head to the Mediterranean and Persian Gulf, said Navy spokesman Lt. Jeff Gordon. 

"The problem with this round of exercises has been that the current administration (in the Puerto Rican government) has actively tried to prevent the maneuvers," Gordon said. "We've also spent a lot of time looking for protesters on the range." 

Monday's maneuvers were stalled for hours after a report that protesters were burying themselves in the 900-acre firing range littered with unexploded ammunition. No one was found. 

The Navy says the range provides unique training that saves American lives in combat. It denies the claims of opponents that 60 years of bombing and shelling have harmed islanders' health. 

White House spokesman Ari Fleischer, asked where President Bush stands on Vieques, said the president's concern was "making sure that American troops are able to carry out their missions." 

"And the line of responsibility for making certain that our troops are able to carry out their missions falls to the Department of Defense," added Fleischer, who spoke at a briefing Monday. 

More than 160 protesters have been arrested since Thursday. Many were charged Monday with trespassing and ordered to pay bail ranging from $3,000 for first-time offenders on Vieques to $10,000 for those convicted in previous protests. 

Among them were environmental lawyer Robert F. Kennedy Jr., Mexican-American actor Edward James Olmos, New York labor leader Dennis Rivera, U.S. Rep. Luis Gutierrez and Puerto Rico opposition Sen. Norma Burgos. 

For decades, the Navy owned the eastern end of the island, which includes the bombing range, and the western end, where it had a munitions warehouse. Sandwiched between the two is an area with 9,400 civilians. 

On Monday, the Navy relinquished its 8,100 acres in the west as part of an agreement reached last year with the White House to quell rising tensions. It gave 4,248 acres to the Vieques municipality, 3,100 acres to the U.S. Department of the Interior and 800 to the private Puerto Rico Conservation Trust. 

But protesters — who have put themselves in the line of fire of the inert bombs to delay exercises daily since they began Friday — continued demonstrating, calling for the Navy to leave for good. 

There has been opposition to the Navy on Vieques since it took over two-thirds of the island during World War II, forcing about two-thirds of residents off their land. 

Simmering resentment exploded after two off-target bombs killed a civilian guard on the range in April 1999, uniting Puerto Ricans in protest and fanning anti-U.S. sentiment. 

Demonstrators occupied the range for a year until federal marshals removed them and the White House brokered an agreement under which the Navy now uses only inert ammunition. 

Also under the agreement, Vieques residents are to vote in November on whether the Navy should stay on the island or leave by May 2003.