* U.S. argues judge's ruling would hurt terrorism fight
* Journalists say detention law could get them locked up
By Bernard Vaughan
NEW YORK, Feb 6 (Reuters) - The U.S. Justice Department urged an appeals court on Wednesday to reverse a judge's decision blocking part of a law allowing indefinite military detention, a ruling that the government has said would hurt its ability to fight terrorism.
A government lawyer told the 2nd U.S. Circuit Court of Appeals in New York that concerns by some journalists and activists, who fear their interactions with groups such as al Qaeda or the Taliban could get them locked up under the provision, were unfounded.
"This statute does not apply to them," Robert Loeb, a Justice Department attorney representing the Obama administration, told a three-judge panel in a packed courtroom.
He also called the earlier ruling "fundamentally flawed."
The government is appealing a Manhattan federal judge's decision last year in a lawsuit brought by journalists including Pulitzer Prize-winner Chris Hedges and activists whose work relates to overseas conflicts.
In the lawsuit, the plaintiffs argued they could be detained indefinitely under a section of the National Defense Authorization Act, a law that Congress passes annually to fund the Defense Department. The provision empowers the government to detain people it deems to have "substantially supported" al Qaeda, the Taliban or "associated forces."
Hedges testified in March 2012 that his concerns over the law chilled his work, which has involved interviewing members of al Qaeda and other groups the United States labels terrorist organizations.
In September, U.S. District Judge Katherine Forrest issued a permanent injunction preventing the United States from invoking the part of the law authorizing indefinite detentions, after granting a temporary injunction in May.
Forrest, whom Obama appointed to the federal bench in 2011, had found the provision violated the Constitution in part because its language is too vague.
U.S. WAR EFFORTS
But the Justice Department has said her ruling would harm U.S. war efforts abroad. It won an emergency suspension of the ruling in September while the appeals panel considers the issue.
In arguments to the court on Wednesday, Carl Mayer, an attorney for Hedges, attacked the government's contention that the provision merely reaffirms powers granted by the Authorization for Use of Military Force, a law passed after the attacks of Sept. 11, 2001.
There is no reason to pass a law to say another law exists, he said.
Mayer also disputed a government argument that another section of the law clarifies that the controversial provision does not alter existing detention law, saying it was vague and did not explicitly exempt people like his clients.
Loeb, the Justice Department lawyer, argued that the government has exercised these detention powers for 10 years without subjecting such people to indefinite detention.
But Judge Lewis Kaplan, a U.S. District judge in Manhattan who is sitting on the appeals panel, appeared skeptical on this point. He said it's always possible the government could change course in the future.
"The executive branch has been known on occasion to change its mind, has it not?" he said.
About 100 protesters assembled outside the court in support of the plaintiffs.
"I think it's wrong to detain people indefinitely without a trial," said Eve Gilbert, 45, of Hackensack, New Jersey. "I don't even care what they did. We have to do better as Americans." (Reporting By Bernard Vaughan; Editing by Cynthia Johnston and Eric Beech)