Assistant District Attorney Isabel Pauley said the four were members of an anarchist military group called FEAR, which stands for "Forever Enduring, Always Ready."
"FEAR structured their organization, plotted attacks and acquired the means to carry out the attacks," WSAV-TV, Savannah, quoted Pauley as saying.
The prosecutor alleged the group had thousands of dollars worth of weapons and its plans included "forcibly taking over the ammo control point at Fort Stewart to take over the post, bombing vehicles of state and local judicial and political figure heads and federal representatives to include the local department of Homeland Security, and bomb fountain at Forsyth Park in Savannah."
One of the defendants, Michael Burnett, a soldier stationed at Fort Stewart, pleaded guilty Monday in the slaying last December of former soldier Michael Roark and Roark's 17-year-old girlfriend, Tiffany York, WSAV-TV said.
Authorities said Roark allegedly had been a member of the militia as well, but Burnett said the group feared he was "a loose end" who might become a problem.
The other three Fort Stewart soldiers were identified as Isaac Aguigui, Anthony Peden and Christopher Salmon. The Army said Peden is a sergeant and the other three are privates.
The wife of one of the soldiers also has been charged in the case, WSAV-TV said.
Burnett, who is to receive a 50-year prison term in return for his testimony against the other defendants, told the court FEAR's goal was to "give the government back to the people."
The Fort Stewart public affairs office issued a statement saying the military post "does not have a gang or militia problem." The statement said the military criminal investigations branch actively investigates any suspicions of gang or extremist group activity.
"We believe the reason we are able to maintain a LOW gang criminal threat status is because of the awareness of and focus on the threat," the statement said.