Flathead County Sheriff Jim Dupont said the group's — alleged ringleader, 38-year-old David Burgert, was being held in the Flathead County jail on charges of assaulting a peace officer and jumping bail.
His girlfriend, 32-year-old Tracy Brockway, is being charged with obstruction of justice for hiding Burgert.
Dupont said Burgert was expected to be charged with an array of crimes related to "Project 7", the latest militia group to surface in Montana, long known as a refuge for anti-government activists ranging from the Freemen to Unabomber Ted Kaczynski.
Police said Burgert and his nine-member group were apparently plotting a series of bloody attacks against local and state officials, possibly as early as this summer.
The objective, officials said, was to force the state to call out the National Guard - who would then become the targets of a wider resistance effort which ultimately would cause the downfall of the U.S. government.
"Apparently, on a certain day, by going out and killing people, they were going to trigger a revolution that would bring down the U.S. government," Dupont said.
Dupont said the plot came to light several weeks ago when he was approached by a member of the group who offered to serve as an informant.
Sheriff's officers searching for Burgert found him at Brockway's home, but after a 24-hour standoff the officers, fearing a shootout, allowed the couple to leave, but their pickup truck became stuck in a snowbank and they were arrested.
A search of Burgert's home turned up the cache of weapons including automatic machine guns, snare bombs, thousands of rounds of ammunition and survival gear as well as a list of the group's alleged targets, who included several judges, the county sheriff, and two deputy district attorneys.
Dupont said that the the FBI had joined local officials in the investigation, which he described as still in its early stages.
He said that Burgert had been a well-known anti-government activist in the Kalispell area, a scenic area of northern Montana near Glacier National Park.
"Anything involving the government, he was against," Dupont said. "These people are scary, because they have a cause and they believe in it."