NEWPORT -- When the Navy stored hundreds of thousands of pounds of TNT on Rose Island between World Wars I and II, an accident could easily have blown the roof off the low-slung, rock solid building housing the explosives.

Ultimately, however, incremental natural forces -- not sudden incendiary ones -- have taken their toll on the historic Fort Hamilton barracks. Wind, water, age and neglect are threatening to ruin the 206-year-old structure, jeopardizing one of the oldest surviving coastal fortifications in the country.

"We need to replace the roof, or we're going to lose the building," says Charlotte E. Johnson, executive director of the Rose Island Lighthouse Foundation.

Fortunately, in true military fashion, reinforcements are on the way. The foundation is a recipient of a $100,000 grant from the state Historical Preservation and Heritage Commission, the largest amount the agency hands out in its annual awards.

The grants, which were given to seven other East Bay preservation projects, were announced yesterday at a news conference at the International Yacht Restoration School in Newport, one of the recipients.

Across the harbor and out in the bay, the Fort Hamilton barracks is hunkered down on Rose Island. The 210-foot long building was built from 1798 to 1800, with nine vaulted chambers and shared chimney. With its 3- to 4-foot thick walls, it was designed to be bombproof, providing shelter for the troops stationed there.

When the 20th century arrived with its two world wars, the barracks became part of the Navy's Torpedo Station. Explosives made on Goat Island were stored here, said Johnson.

"They were still considered bombproof structures -- only the bombs were put inside," said Johnson.

After World War II, the buildings were abandoned. The lighthouse, which was built in 1870 upon one of the fort's bastions, remained in use until the Pell bridge was built in 1970. No longer needed as a navigational aid, its light was extinguished.

Since 1984, the Rose Island Foundation has been striving to preserve and protect the island and its historic structures. The lighthouse was its first priority. It was refurbished and automated, allowing it to be relit in 1993.

Now the foundation is embarking on a campaign to raise $1 million for an endowment fund and another $1 million for additional improvements to the lighthouse and to other fort buildings. Among the projects is replacing the barracks' old asbestos shingle roof for $475,000.