“There are people inside,” said James P. Delgado, director of maritime heritage at the , which monitors the wreck.

His agency, an arm of the Commerce Department, has released to the news media an image from 2004 that shows a boot on the seabed near what the agency calls a coat. “The articulation of the coat and boots are highly suggestive of someone coming to rest here,” Mr. Delgado said by e-mail. “This is the first full release of the whole image and the first explicit captioning.”

The bold federal assertions are dividing Titanic experts. The most experienced divers say they doubt that bodies lie intact in unexplored compartments of the deteriorating ship.

“I’ve seen zero human remains,” , the moviemaker and explorer, who has visited the wreck 33 times and extensively probed its interior, said in an interview.

“We’ve seen clothing,” he added. “We’ve seen shoes. We’ve seen pairs of shoes, which would strongly suggest there was a body there at one point. But we’ve never seen any human remains.”

Right now, of course, is an excellent time for federal officials to press their concerns and make their case for new protections.

Sunday is the centenary of the sinking, and — not coincidentally — Senator John Kerry, the Massachusetts Democrat, has introduced a bill that would give the Commerce Department new supervisory powers to protect the Titanic wreck site from salvagers and intrusive research.

The fight for protection began shortly after the Titanic was found in 1985 more than two miles down at the bottom of the North Atlantic, upright but split in two. The international waters ensured a long struggle over legal jurisdiction — even as salvagers made off with thousands of artifacts.

In 1986, Congress passed a protective law known as the , but officials at the ocean agency and elsewhere agree that it has no teeth. In 2004, the United States, France, Canada and Britain signed a draft treaty for better safeguards. But it has never been approved because it requires legislative support — which the Kerry bill would provide.

While seeking to enhance their custodial role, federal officials are now pressing the question of the missing dead. After the Titanic sank, searchers recovered 340 bodies. Thus, of the roughly 1,500 people killed in the disaster, about 1,160 bodies remain lost.

In an interview, Dr. Delgado of the ocean agency said the muddy seabed showed “clear signs” of human imprint. “Yes, you don’t see much in the way of bone,” he said, referring to the newly released photograph. “But this is clearly where someone came to rest on the bottom. It speaks powerfully to it being a grave site.”

Paul H. Nargeolet, a French mini-sub pilot who has visited the Titanic 30 times — the second-most experienced diver, after Mr. Cameron — said he had never seen any human remains.

Skeptics say that federal officials are exaggerating scanty evidence in an effort to expand their powers.

“It’s a legal tactic,” said David G. Concannon, a maritime lawyer who has dived to the Titanic’s resting place and advised the Explorers Club. “The opponents of salvage want to equate it to a grave site.”

But Mr. Delgado of NOAA defended his agency, saying: “We’re not pushing for bureaucratic turf. We’re pushing for international cooperation to protect the wreck.”

Scholars say most of the people who died were probably in life jackets and swept far to sea by wind and waves. After the sinking, a storm blew up that was reported to have scattered bobbing corpses in a line 50 miles long.

But some Titanic historians argue that as many as hundreds of people were trapped inside the sinking ship.