The battleship USS Maine blew up 100 years ago in Havana Harbor, taking 266 souls and triggering a chain of events in the launching of the American empire. But now, 100 years to the week after the disaster prompted Congress to declare war, there is fresh debate about what really happened. What sank the Maine? Was it a mine, or was it an accident?

Yesterday, at a U.S. Naval Institute meeting in Annapolis, more than 250 people, including naval historians and maritime engineers, listened as experts vigorously debated the issue in reaction to a recent National Geographic study that reopened the question. Some declared a mine could have sunk the Maine; others insisted it was impossible. The only thing that is clear is that the controversy is far from over.

"It's generated incredible interest," said Fred Schultz, editor of Naval History, the institute's magazine. "It's kind of like the Titanic."

A Web page set up by the institute about the Maine report has generated the most hits in the naval magazine's history, institute officials said.

"The fate of the Maine comes to this: Did a mine start the war, or did an accident?" said Thomas B. Allen, author of the National Geographic article and moderator of yesterday's panel. "If it was an accident, then the war shouldn't have happened."

For the last two decades, most historians have accepted a 1976 study commissioned by Adm. Hyman Rickover that found no evidence of a mine and concluded the Maine was sunk by an internal explosion, most likely a fire in a coal bunker that ignited a nearby store of ammunition.

National Geographic in its February issue published the results of a study it had commissioned into the sinking.

Under a headline declaring, "New Interpretation Throws Open the Question of Cause," a report on the study said that computerized technology unavailable to earlier investigators revealed that the explosion could have been caused by either a mine or an accidental fire.

Among naval historians and engineers, the claims sparked a furor. Critics have accused the magazine of ignoring some key facts and claimed the study turned up little new.

"The Geographic was accused of being irresponsible for even raising the issue," Allen said.

"I was accused of trying to change history," said David Wooddell, a senior researcher for National Geographic. He added that National Geographic has "a reputation of evenhandedness."

The Maine was on a show-the-flag mission to Spanish-ruled Cuba in response to unrest. It was torn apart Feb. 15, 1898, by a massive explosion as it lay at anchor. The blast generated enormous outrage in the United States, where public opinion, fanned by William Randolph Hearst's newspaper coverage, blamed Spain.

A month later, a U.S. Navy court of inquiry ruled that a large mine was responsible. On April 25, Congress declared war on Spain.

The war was short and decisive. After it ended in July, the United States was left with the makings of an empire, including Cuba and the Philippines.

The trauma of losing the Maine -- the death toll was the largest loss of life the U.S. Navy would suffer until Pearl Harbor -- was not forgotten.

In 1911, the U.S. Army Corps of Engineers built a cofferdam around the wreckage and eventually raised the Maine from its grave site. After examining the wreckage, a Navy board again concluded a mine had sunk it.

The Maine was then towed to sea, and with an American flag flying on its bow, allowed to sink again, presumably forever. But doubts about the official findings persisted. Spain insists to this day that the explosion was an accident.

Rickover, the father of the nuclear Navy, became interested in the debate after reading a 1974 newspaper article. The team of experts he assembled found no evidence of a mine and concluded in a 1976 report that "an internal source was the cause of the explosion." The accident finding, backed by Rickover's stature, was accepted as authoritative. Textbooks in the United States were revised to reflect the findings.

"Rickover ended the debate," said Allen, author of a biography of the admiral. "So, for anyone to say, Wait a minute,' is to challenge Rickover and his memory."

The challenge raised by National Geographic was under close scrutiny at yesterday's debate.

Shriver Hering, a consultant involved in the National Geographic study, gave a technical report on the findings. "It could have been a mine, and we can't rule it out," Hering said. The structural failure seen in photographs "is consistent with a small black powder mine."

But panelist Ib Hansen, who directed the Rickover study and who recently retired from a top position at the Naval Surface Warfare Center at Carderock, gave no quarter. "There was no mine under the Maine," Hansen said.

In a recent paper written with Dana Wegner, the Navy's curator of ship models at Carderock, Ibsen said, "Perhaps a mystery' is more fascinating than the truth."

But the mystery is likely to linger. "There are a lot of people who say the case is closed," Schultz said. "It is about as wide-open as can be." CAPTION: On Feb. 15, 1898, the battleship USS Maine sank in Havana Harbor, killing 266 crewmen and precipitating the Spanish-American War. A National Geographic report has reopened the debate on what caused the ship to sink.