Less than two weeks before it must decide which parts of the Pentagon's base-closing plan to change, an independent commission is struggling over what to do with the Air Force's plan to restructure the Air National Guard.

When the nine-member panel meets later this month, Chairman Anthony Principi (search) said it "will be compelled to exercise its best judgment" on whether to sign off on the plan to shake up dozens of Air Guard units.

During a hearing Thursday, Principi questioned whether the Air Guard plan would mean new risks for the United States' domestic security. "We're proposing taking aircraft out of a number of states, eliminating all of the assets out of certain states and dramatically reducing them in other states," he said before asking Pentagon officials to consider the consequences to security on the homefront.

Defense officials tried to reassure Principi and other skeptical commissioners.

"Our responsibilities to support the Department of Homeland Security (search) in their homeland security mission are not impacted adversely by this beyond a level of acceptable risk," Peter Verga, a deputy assistant secretary of defense, told commissioners.

Adm. Timothy Keating, commander of the U.S. Northern Command and the North American Aerospace Defense Command, said: "It poses no unacceptable risk."

Commissioners appeared unconvinced.

"That's not exactly a wholehearted endorsement," Harold Gehman (search), a retired Navy admiral, said.

The Air Guard proposal has emerged as the most contentious part of Defense Secretary Donald H. Rumsfeld's proposal to close, shrink or expand hundreds of military bases and other installations nationwide. So Principi gave the Pentagon and states one last chance to argue their cases about it before the panel sends its final report to President Bush next month.

The plan calls for shifting people, equipment and aircraft among at least 54 sites where Air Guard units now are stationed. Roughly two dozen sites would expand, while about 30 would be closed or downsized. In many cases, units would continue to exist but no planes would be assigned to them.

The Air Force says units without planes would receive new non-flying missions and also would retain their roles in supporting the needs of governors during statewide emergencies.

For their part, state adjutants general, who oversee the Air Guard in the states, argued that the plan would prevent units from fulfilling their homeland security missions, including protecting the skies and supporting governors in state emergencies.

Maj. Gen. Roger Lempke, president of the Adjutants General Association of the United States, said the proposal would take the Air National Guard down an uncertain path, leading to a "ripple effect on personnel, readiness and an inability to support homeland security needs, which in our view would be irreversible."

He urged the commission to review an alternate proposal the group offered.

The Pentagon says the Air Guard changes are part of an overall effort to reshape the Air Force — which is to have a smaller but smarter aircraft fleet in the future — into a more effective and efficient force by putting active duty, Air Reserve and Air Guard units to work alongside one another.

Two states, Pennsylvania and Illinois, have sued over the Air Guard proposal arguing that the Pentagon doesn't have the authority to move units without each governor's consent. The Pentagon disagrees. A commission spokesman said the commission has received an opinion from the Justice Department (search), but neither the spokesman nor commissioners would disclose what it says.