* Obama lawyers try to reinstate individual mandate
* Court to weigh whether entire law should be struck down
* Court's ruling may influence other healthcare cases (Adds details from oral arguments)
By Jeremy Pelofsky and Lisa Lambert
RICHMOND, Va., May 10 (Reuters) - A U.S. appeals court on Tuesday sharply questioned whether the state of Virginia could challenge President Barack Obama's signature healthcare law, which requires Americans to buy insurance.
Virginia passed a law barring the federal government from making its citizens buy insurance, and in December the state won a federal judge's ruling that the insurance purchase requirement was unconstitutional.
The case is the first to reach oral arguments at a federal appeals court and experts have said a ruling here could influence other pending challenges to the healthcare law, including a June 8 hearing by another appeals court. <^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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A three-judge panel of the U.S. Court of Appeals for the Fourth Circuit on Tuesday questioned whether a state could pass a law to buck a federal mandate, saying that could lead to states challenging many other federal requirements, such as sending troops to war.
"A state could challenge any federal statute in court as long as the state passed a law?" asked Judge Diana Motz. All three judges hearing the case were appointed by Democrats, including two by Obama.
Lawyers for Virginia countered that that the healthcare law threatened the state's sovereignty and that the state law was an attempt to protect its citizens.
"The flip side is that state can't sue ever," Duncan Getchell, solicitor general for Virginia told Motz. "I don't know why it's a low trick to pass a law."
The healthcare law passed last year was a major victory for Obama, one that the Republican party is working to undo in the courts, statehouses and Congress.
Obama's Republican opponents are expected to make the issue a theme during his 2012 reelection bid by arguing it is a costly and unnecessary government expansion. They have already sought to repeal and choke off funds for the law in Congress.
The Obama administration's top appellate lawyer, acting U.S. Solicitor General Neal Katyal, told the appeals court that allowing Virginia's challenge to go forward would inject the states into the federal courts over "abstract political disputes."
The U.S. Court of Appeals for the 11th Circuit on June 8 will weigh the Obama administration's appeal to a decision that struck down the entire healthcare law as sought by 26 states. (Editing by Vicki Allen)