GAINESVILLE —Two Georgia men pleaded guilty Tuesday to conspiring to get an unregistered explosive and an illegal gun silencer in what prosecutors describe as a plot to attack government targets.

The suspected ringleader of the group, Frederick Thomas, and Dan Roberts entered their pleas at a hearing in federal court in Gainesville, about 55 miles northeast of Atlanta.

Thomas, 73, and Roberts, 67, could face up to five years in prison and a $250,000 fine. They also agreed to cooperate with authorities.

They are among four men arrested in early November after at least seven months of surveillance by an undercover informant who infiltrated their meetings at homes, during car rides and a Waffle House restaurant. Ray Adams, 55, and Samuel Crump, 68, are charged with conspiring and attempting to make ricin.

The government’s case is pinned on dozens of hours of recordings of the men talking about their anti-government views with an undercover informant and what kind of attacks they could carry out.

In the tapes, the four allegedly boasted of a list of government officials who needed to be “taken out”; talked about scattering ricin from a car speeding down a highway past major U.S. cities; and scouted tax offices. At one point, Thomas said, “We’d have to blow the whole building like Timothy McVeigh,” a reference to the man executed for bombing a federal building in Oklahoma City in 1995, killing 168 people.

U.S. Attorney Sally Quillian Yates said the men are members of a “fringe militia group” who planned attacks on innocent citizens, conducted surveillance on government buildings and took concrete steps toward carrying out the attacks.

“This case demonstrates that we must remain vigilant in protecting our country from citizens within our own borders who threaten our safety and security,” she said.

Defense attorneys said the conversations were taken out of context and that the men were actually planning to unite various militia groups across Georgia to create a legitimate “governor’s army” that would be at the state’s disposal.