By Basil Katz

NEW YORK, Nov 5 (Reuters) - A U.S. appeals court on Monday questioned whether the federal government had overstepped its bounds in a sting operation against four men who were convicted of placing what they thought were bombs at New York synagogues.

The four, arrested in an FBI sting operation in May 2009, were sentenced in June 2011 to mandatory minimum terms of 25 years in prison. A Manhattan federal court jury found them guilty after a two-month trial in 2010.

The case against the "Newburgh Four," named after their hometown of Newburgh, north of New York City, was announced by U.S. authorities with much fanfare.

It has since become a poster case for critics of government sting operations who say the tactics can lead to the illegal entrapment of defendants. The U.S. Justice Department counters that such investigations have strict guidelines and that they are an essential tactic to combat terrorism.

Defense lawyers have asked the 2nd U.S. Circuit Court of Appeals in New York to throw out the convictions of the four defendants. At Monday's two-hour hearing, a three-judge panel peppered defense attorneys and the government with questions.

Chief Judge Dennis Jacobs asked prosecutor Adam Hickey if he knew of another case where the government's role in "creating, animating the offense was so all encompassing?"

"What distinguishes this case is not so much the government's involvement, it's the gravity of the conduct," Hickey responded.

Lawyers for the four defendants argued that their clients were entrapped and their due process rights were violated.

"The case was not so much about terrorism but about the power of the government to use a corrupt informant to entrap U.S. citizens in a crime they never would have or could have committed," said Clinton Calhoun, who represents James Cromitie, 46, the main defendant in the case.

The defense lawyers said their clients were badgered into committing to the bogus plot by a confidential informant, Shahed Hussain, who posed as an Islamist militant.

"James Cromitie indicated that he was trying to be a good Muslim ... and it is Hussain who is forcing him to action," Calhoun told the judges.

Hussain, a Pakistani motel owner, had participated in other FBI investigations in the past. Cromitie was a low-level drug offender who had a night-time job restocking shelves at a Walmart, according to court documents.

Defense lawyers said Hussain manipulated Cromitie's affection for him and encouraged Cromitie to carry out a conspiracy to bomb synagogues and to shoot down military planes at an Air National Guard base in Newburgh, New York, with Stinger surface-to-air missiles.

Judge Reena Raggi appeared unconvinced that Cromitie's due process rights had been violated, saying poor and uneducated people were sometimes recruited by Islamist militants to commit violent acts thanks to misleading religious ideas and promises of wealth.

"I'm not sure this rises to the level of outrageous government misconduct," she said.

The other defendants are David Williams, 31, Onta Williams, 36, and Laguerre Payen, 31.

The appeals court said it would issue a decision at a later date.

The case is US v. James Cromitie et al., U.S. Court of Appeals for the 2nd Circuit, No. 11-2763.

For the government: Adam Hickey, Assistant U.S. Attorney.

For James Cromitie: Clinton Calhoun of Calhoun & Lawrence.

For Onta Williams: David Lewis, Federal Defenders of New York.

For David Williams: Theodore Green of Green & Willstatter.

For Laguerre Payen: Samuel Braverman of The Law Office of Samuel Braverman.

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