Their guilt isn't in question. The six men and four women already admitted being involved in a series of arson fires that did $40 million in damage to research facilities, a ski resort and other businesses in the West. But are they terrorists?

A federal was to hear arguments Tuesday on a motion by the government to add a so-called terrorism enhancement to their sentencing.

Prosecutors want Judge Ann Aiken to declare the group terrorists — something defense attorneys argue has never happened in 1,200 arsons nationwide claimed by Earth Liberation Front and Animal Liberation Front.

The defense argues that branding their clients terrorists is more about politics than sentencing.

"The Government has Attorney General Alberto Gonzales' political agenda to advance with this case, and nothing else to lose if the Court declines to impose the enhancement," wrote attorney Terri Wood, who represents Stanislas G. Meyerhoff.

Meyerhoff faces the stiffest sentence recommendation for his involvement in seven fires and the toppling of a high-tension power line. The terrorism enhancement question will be settled in his case and, under an agreement with all parties, applied to the remaining defendants. Each has pleaded guilty to charges of conspiracy and arson.

A ruling that the 10 are terrorists is not likely to boost the time they spend behind bars — the prosecution recommends three to 16 years — but it could land them in tougher prisons.

The fires targeted forest ranger stations, meat packing plants, wild horse corrals, lumber mill offices, research facilities, an SUV dealer and, in 1998, Vail Ski Resort. No one was injured, the defense notes in legal motions.

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The case, known as Operation Backfire, is the biggest prosecution ever of environmental extremists, and has turned on its head the prevailing idea that arsonists have generally acted alone, said Brent Smith, director of the Terrorism Research Center at the University of Arkansas.

"We thought these people operated for the last 15 years under this kind of uncoordinated violence approach, just like the extreme right was doing — leaderless resistance," Smith said. "That's why this case is so very different."

Prosecution filings argue that though the defendants were never convicted of terrorism, they qualify for the label because at least one of the fires each of them set was intended to change or retaliate against government policy.