The man accused of masterminding a plot to blow up two synagogues in the Riverdale section of the Bronx was offered $250,000 by a paid government informant for his effort, according to papers filed in court on Wednesday by defense lawyers.

The papers, which seek dismissal of the federal charges, detail how the informant spent nearly a year courting the man, encouraging him to identify targets and recruit others to the mission. The informant, identified in the court papers as Shaheed Hussain, who had helped the Federal Bureau of Investigation in at least one other case, has been credited with helping to prevent the plot’s success.

Mr. Hussain posed as a wealthy representative of a Pakistani terrorist organization. He repeatedly dangled the promise of large cash payments as he helped oversee the recruitment of the four men arrested last May in the plot, according to the court papers, which draw from recorded conversations.

During one conversation last April, James Cromitie, the Newburgh, N.Y., man accused of leading the plot, told Mr. Hussain that he was out of the state trying to make money. The two had not spoken for six weeks, and Mr. Cromitie expressed reluctance at joining Mr. Hussain’s plan.