Even as the first ships of a carrier battle group steamed toward controversial training exercises, President Clinton yesterday hammered out the broad terms of an agreement to allow the Navy to resume use of its Puerto Rican firing range on a temporary and limited basis, senior officials said.

Although talks are still underway and the consensus is fragile, Clinton and Attorney General Janet Reno also discussed the possibility of sending FBI agents to remove protesters who are occupying the firing range on the small island of Vieques, officials said.

Even if the White House can satisfy Gov. Pedro Rossello and other top Puerto Rican leaders, dozens or even hundreds of demonstrators may engage in civil disobedience to publicize their cause, according to participants in the anti-Navy protest.

To resolve the impasse it acknowledges helping to create, the Navy has agreed to end all exercises on the firing range by a specific date in the next three to five years, the officials said. But differences remain over whether live ammunition or only nonexplosive "inert" ordnance can be used in the interim, particularly during training exercises for the battle group led by the USS Eisenhower, which are scheduled to begin next week, officials said.

The administration has been on the brink of announcing a deal at least twice in the past few days, only to pull back because of the Navy's insistence on live ammunition and Puerto Rican leaders' insistence on dummy bombs, the officials said.

Vieques has served as a major training ground for the Atlantic Fleet since 1941, and the Navy contends that the 52-square-mile island is the only place that Marines can practice amphibious landings while surface ships and aircraft provide support with live ordnance. Such training has been suspended since April 19, when two stray bombs killed a civilian security guard at an observation post on the fringe of the firing range.

The accident last April galvanized public opinion in Puerto Rico against use of the firing range, and the island's usually fractious political leaders have stood together behind the demand that Vieques never again serve as a target for any kind of bombing. The Puerto Ricans argue that the Navy has broken written agreements regarding aid for the 9,300 residents of Vieques, violated limits on the use of the firing range and reneged on promises to reduce environmental and health hazards.

The Navy admits that it has not been an ideal neighbor and has promised better behavior in the future. But it drew a line in the sand by proclaiming publicly this fall that the lives of service members will be needlessly endangered if it is denied access to Vieques.

Clinton began maneuvering between these two antagonists on Veterans Day, and the pace of his efforts stepped up this week as the first few ships of the Eisenhower battle group left their home port of Norfolk for final training at Vieques before a six-month deployment to the Mediterranean.

Since Monday, Clinton has spoken to Rossello three times, and the governor has signaled his willingness to compromise on an agreement to allow training with inert ordnance if the Navy phases out its use of the firing range completely over the next few years.

At a briefing yesterday, Rear Adm. Craig Quigley, a Pentagon spokesman, reaffirmed the military's stance that live fire training is irreplaceable. "But there are ways that you can accomplish that, and there are other ways to do things that are all part of the ongoing discussions right now," he added.

A Pentagon official said the Navy could agree to inert ordnance exercises but only as a short-term solution and would insist on some live fire training at Vieques during the phase-out period.

If Clinton can work out a deal between the Navy and the Puerto Rican government, he will still have to deal with the protesters camped out at about a dozen sites on the firing range. "On Vieques there is a firm determination that the protesters will only leave if the Navy leaves first. Otherwise, they will have to be forcibly removed," said Manuel Mirabal, president of the National Puerto Rican Coalition, a Washington-based public policy group.

During a meeting at the beginning of this week, Clinton and Reno discussed how the protesters might be handled, and Reno told the president she was not in favor of sending FBI agents, administration officials said. However, Justice Department officials said they would dispatch the FBI if Clinton gave the order to do so.

While other options also are under consideration--such as sending members of the U.S. Marshals Service--the FBI has the necessary resources and training to do the job, officials said.