WASHINGTON — For 65 years, the wreck of the USS Arizona has been leaking oil from its grave at the bottom of Pearl Harbor, staining the water, visitors often say, as if it were the ship's blood.

The leaks come from about 500,000 gallons of thick, bunker C fuel oil that remain trapped in the deteriorating hulk — oil whose "catastrophic" release experts now think is inevitable.

Even as the nation recently observed the 65th anniversary of the attack that plunged the United States into World War II, scientists at a federal research center in Gaithersburg, Md., are trying to predict when the release might happen. In five years? Or 50? And to do that, they are building a model of the ship: not of plastic and glue, but of data.

The experts at the National Institute of Standards and Technology think it is the first mathematical model to simulate the deterioration of a sunken ship and could be used to predict the deterioration of hundreds of wrecks around the country.

Similar models, which are run with ultra-powerful computers, are used to forecast the weather, design cars and simulate crashes.

"To my knowledge, nobody has published or spoken of modeling the deterioration of sunken ships," said Timothy Foecke, a metallurgist at the institute who is supervising the work.

"What we're trying to do is ... predict stability of shipwrecks," Foecke said. "In particular, we're working on the Arizona, but it also has application to hazardous wrecks ... all around the coast, dating back to World War I. There's ships with munitions, with hazardous cargoes, with all kinds of different things."

The work is part of the USS Arizona Preservation Project, headed by the National Park Service and the USS Arizona Memorial.

"The overall project goal is to model and characterize the deterioration processes ... to predict when we may have potential structural collapse," said Matthew Russell, project director. It is impossible to remove the oil from the ship because that would disturb what he said is "an enormous tomb."

READY TO SAIL

On Dec. 6, 1941, the Arizona took on 1.2 million gallons of heavy fuel oil at its berth in Pearl Harbor. The ship was scheduled to make a Christmas trip back to the West Coast the next weekend. The fuel, which was so heavy it had to be atomized for use in the engines, weighed 4,000 tons and was stored in more than 200 tanks, or bunkers, spread across four deck levels throughout the vessel.

In the Japanese attack the next morning, a 1,700-pound bomb plunged through the ship's deck, detonating in an ammunition compartment. The explosion obliterated a section of the Arizona's bow, blasted backward toward the stern and vented out the smokestack. It also set much of the oil on fire, burning for three days.

The battleship — three times the size of the Statue of Liberty — settled to the bottom in 34 feet of water, along with the bodies of more than 1,100 sailors and Marines.

The Arizona, which was launched in 1915, is 91 and has been submerged for six decades.

Science is not sure how the metal in old ships fares for long periods under water.

The Civil War submarine CSS H.L. Hunley, which sank in 1864, was surprisingly intact when it was raised from the protective mud off the harbor of Charleston, S.C., in 2000.

The turret of the USS Monitor — which sank in the Gulf Stream off Cape Hatteras in 1862 — was in worse shape when it was recovered in 2002.

COMPUTER MODEL

Sooner or later, though, submerged metal wrecks are reduced to "an iron ore deposit," Foecke said.

To assess that process on the Arizona, he and guest institute scientist Li Ma have built a "finite element model." They took the ship's blueprints, carved out an 80-foot section from the middle and entered its dimensions into a computer.

They then used special software to break the section into about 200,000 data blocks, or elements, and entered what they knew about the properties of the metal, corrosion and damage.

Scientists also entered into the model what they knew about external forces on the vessel: such things as pressure from the water, the bottom, gravity and waves.

The result is like a single frame from a movie, Foecke said, and it then becomes possible to play the movie, by adjusting the data, and see how it might turn out.

Foecke, who keeps pieces of the Arizona's steel hull in an office safe, says the model is not perfect.

It "will give us a time frame within which we can expect (the ship's) failure and the general type of failure — upper decks breaking down, lower decks erupting up, hull tipping in or out — but not exactly where," he wrote in a recent e-mail.

CORROSIVE INSTABILITY

Foecke said an early version of the model has been run, gradually "corroding" the metal thickness in small increments. When it was thinned 75 percent, parts of the structure grew unstable, but that kind of corrosion is not expected to happen for 10 or 20 years, he said.

"We think that nothing serious is going to happen for about 10 years, plus or minus years," Foecke said.

When the structure collapses, Foecke said, the oil will "erupt" toward the surface.

"It's going to break the wreck up and open," he said. "The oil does have buoyancy, and it's trying to find a way out, and there's quite a lot of it."

Even though Pearl Harbor is fairly industrialized, Foecke said, a big leak would create "a huge mess."

A spill of 100,000 gallons of jet fuel in 1987 fouled a mangrove swamp and a wildlife refuge, and took two months to clean up, according to news reports of the time.

Douglas Lentz, National Park Service superintendent of the Arizona Memorial, said extensive plans are in place should a large leak occur.

But Russell, the project director, thinks any Arizona collapse would take place gradually. "There won't be any single, serious collapse that releases all the oil," he said. "But we're trying to get an indication of when the first wave of releases may occur."