The biggest conventional bomb ever built stands balanced on its nose at the U.S. Army Ordnance Museum at Aberdeen Proving Ground.

Call it the world's biggest dud.

Built too heavy for any airplane to carry, the World War II-era T-12 is perhaps the biggest attraction at what was once one of the top tourist sites in northeastern Maryland. But now the bomb - and the thousands of tanks, assault rifles, grenades and other weapons at the museum - could be shipping out.

In one of the lesser noted elements of its plan to close dozens of major bases across the country, the Pentagon wants to move the ordnance museum to Fort Lee, Va., where several Army facilities would be consolidated.

Moving the museum would mark the end of a significant Harford County landmark whose popularity might have waned in recent years but which remains a significant resource for military research and development.

"There are some really one-of-a-kind pieces from World War I," said Harford County Executive David R. Craig, whose now-deceased uncle designed exhibits at the museum in the 1980s. "People don't understand what all that stuff is there for, how important it was for the Army."

The Pentagon's reorganization plan, under review and subject to approval by a federal commission, would greatly benefit Aberdeen Proving Ground. The post stands to see a net gain of more than 2,000 jobs, even with the proposed loss of the Ordnance Center and School, and officials seem resigned to the prospect of losing the museum if the proving ground gains in the long run.

"I join the Aberdeen community in my disappointment in seeing [the Ordnance Center and School] moved to Fort Lee," Sen. Barbara A. Mikulski said in a statement last month. "However, the primary economic impact of the Pentagon's [Base Realignment and Closure Commission] recommendations on APG is the increase of nearly 5,000 jobs."

Meg Wloczewski, who manages the Harford County Tourism Council's visitor center, said the ordnance museum ranks among the county's top three tourist attractions. "To have it leave," she said, "that would be disappointing."

The museum has acquired thousands of artifacts from the U.S. military and other countries. No other place boasts the 43,600-pound T-12 bomb or the German K-5 railroad gun (aka "Anzio Annie"). It also is home to a rare, fully automatic 12-gauge shotgun.

"It is a piece of history and a piece of culture" unique to Aberdeen, said Wyett Colclasure, president of the Army Alliance, a nonprofit group that works to strengthen Aberdeen Proving Ground's economic future. "That's the home of ordnance."

People used to come by the busload to the museum. But after the Sept. 11 attacks, Aberdeen Proving Ground was secured and closed to all but military personnel and Department of Defense civilians. The museum reopened to the public in the fall of 2002, and the number of visitors has gradually crept back up, though not near the average 200,000 people a year who once visited the museum.

Last year, 30,000 people visited. This year, the museum is on track to have 50,000 visitors, said museum director William F. Atwater.

Atwater has an explanation for the steep drop in visitors.

Before Sept. 11, 20 to 30 tour buses a day would visit the museum on their way to bigger destinations along the East Coast. Tour buses no longer visit the museum, save for the occasional bus being rented out for a reunion, such as the reunion of the Battle of Anzio veterans.

"When you can't get the tour buses aboard, you're not going to get the numbers," Atwater said. Atwater, a Vietnam veteran, said tour buses no longer make trips to the museum because of the increased security measures - if one member of a tour group does not have government-issued identification, the bus must either turn around or leave the person at the gate.

But the museum is more than a tourist attraction, Atwater said. It is also a key research facility for engineers studying the evolution of military technology and developing new weapons.

Museum visits are part of the ordnance school's curriculum, which is why the museum would be forced to move with the school to Fort Lee, said Col. Kevin Smith, the center's chief of staff.

Atwater is not necessarily opposed to moving to Fort Lee. For years the museum has sought to raise money to build an indoor home for the tanks, which continually need to be restored, at a cost of about $400,000 a year.