FORT WALTON BEACH, Fla. — A metal box found in the South Pacific, initially dismissed as junk, may be a promising clue to the disappearance of pilot Amelia Earhart, say members of an organization trying to unravel the mystery.

Earhart and navigator Fred Noonan vanished without a trace 53 years ago while attempting to make an around-the-world flight.

Tom Willi and Tom Gannon, both retired military fliers living in this Florida Panhandle city, used 1930s navigation techniques to plot Earhart’s likely course.

They persuaded the International Group for Historic Aircraft Recovery, based in Wilmington, Del., to mount a $250,000 expedition last year to the Pacific atoll Nikumaroro and nearby McKean Island.

TIGHAR’s 28-member team returned with several items, but the most intriguing is the aluminum box, now identified as a navigator’s bookcase. The box, about one foot by one foot by 10 inches, was buried in sand on the atoll and discovered with someone using a metal detector.

Gannon said Friday that he believes the bookcase came from Earhart’s plane.

“It’s more than a promising lead. It’s a convincer,” he told the Northwest Florida Daily News.

But TIGHAR’s president, Patricia Thrasher, was more cautious.

“We aren’t ready to say, `This is it, ta-da!,” she said. “We can’t do that until we see a photograph of it in the Earhart airplane or find somebody who says, `Yeah, I installed one for Noonan.’ But we are very excited about it.”

Researchers have determined the bookcase was manufactured by Consolidated Aircraft Corp. of San Diego for PBY Catalina flying boats, used to resupply a Coast Guard navigation and communications base on now-uninhabited Nikumaroro during World War II.

However, TIGHAR reported in its August newsletter that wartime PBYs carried a later-model bookcase and that the one found by the Earhart expedition had mounting holes and fixtures that “are all wrong for installation in a PBY.”

The researchers have speculated that Noonan could have bought or borrowed a bookcase from the Navy and modified it for use in Earhart’s two-engine Lockheed Electra.

Early versions of the bookcase were available in 1936 and 1937, Thrasher said. Ms. Earhart and Noonan vanished in July 1937.

The organization has been unable to find any photographs or official sketches of the interior of the missing Electra.

“The focus for photographers was always Earhart and that meant the cockpit, not the back of the aircraft where the navigator’s bookcase would’ve been,” she said.

Thrasher said the group plans to return to Nikumaroro in September 1991 to look for the missing plane with remote underwater search equipment.

“If it’s where we think, the airplane is going to be down about 2,000 feet,” Thrasher said.