ELENA, Mont., Feb. 28 ÷ State and federal officials are investigating the case of a man in the northwest section of Montana who is described as part of a right-wing conspiracy to assassinate local police officers, prosecutors and judges.

Sheriff Jim Dupont of Flathead County said officers who raided the trailer of the man, David Earl Burgert, in early February found 30,000 rounds of ammunition, body armor, plastic explosives, machine guns and other weapons. Mr. Burgert, 38, has not yet been charged concerning the weapons cache but is being held on charges stemming from earlier incidents with the police.

Officials said Mr. Burgert was part of a right-wing militia cell, Project 7, a label apparently taken from the number designated for Flathead County on the state's license plates.

Sheriff Dupont said Mr. Burgert hoped that killing police officers and others would bring on a war with the federal government. Many extreme conservatives contend that counties are the only legitimate government and that state and federal governments have no power over them.

Also arrested was Tracy Brockway, 32, who was charged with obstruction of justice for harboring Mr. Burgert. Officials said Ms. Brockway used her job as a cleaning woman at the Whitefish Police Department, a Flathead County town, to gather information for Project 7 on police officers in the area.

Law enforcement officials kept the arrest a secret because they hoped to gain access to encrypted files in a computer owned by Mr. Burgert that might lead to more arrests.

But information about the plot became public at a bail reduction hearing on Tuesday for Ms. Brockway. Officials said the computer code had still not been cracked.

Exactly how large Project 7 is remains unclear; Sheriff Dupont said his research showed there might be nine other members in addition to Mr. Burgert. "They like to keep these militia cells small," he said. He said the F.B.I. and the Bureau of Alcohol, Tobacco and Firearms were also investigating.

According to court documents, Mr. Burgert and his group planned to "ambush and kill law enforcement officers and judges, along with their families.

"The plot also allegedly included bringing militia members into Montana from various areas around the United States," the documents say.

Flathead County, adjacent to Glacier National Park, is home to some of Montana's wildest country, with vast tracts of forest and rugged mountain ranges. Another militia group, called Project 56, operates in nearby Lincoln County, and other associates are in northern Idaho, the sheriff said. But so far they have not been linked to Mr. Burgert.

The authorities said they had found intelligence sheets kept by Project 7 members with information on 26 police officers, including their names and those of their family members as well as where they lived. Mr. Burgert was also believed to be videotaping police officers and their families surreptitiously, the sheriff said.

Mr. Burgert was arrested last year for assaulting a Flathead County sheriff's deputy and in November other charges of obstructing a police officer were brought against him. When a judge ordered him from house arrest to jail at the end of January, Mr. Burgert disappeared and his wife claimed he had drowned. He was found in Ms. Brockway's home on Jan. 31. Carrying a machine gun, Mr. Burgert fled in a vehicle and later on foot. After a four-hour standoff, he surrendered.

A growing right-wing movement in Flathead County has alarmed law enforcement officials and others. John Stokes, a radio station owner in Kalispell, is the host of a talk show in which he excoriates environmentalists, calling them "green Nazis."

Many environmentalists have complained to law enforcement officials that they have been harassed and intimidated.

Mike McGrath, the state's attorney general, said that he had met with citizens who had been threatened and that he believed the attacks had been fueled by Mr. Stokes. "He makes it acceptable," said Mr. McGrath. "It's not good. I don't think it accurately reflects the people of Flathead County or of Montana."

Ken Toole, a Democratic state senator, is the program director of the Montana Human Rights Network, a private nonprofit group in Helena that has studied the growing right- wing movement in northwest Montana and Idaho. Mr. Toole said that while Project 7 was apparently small, many residents in the Flathead Valley felt it was acceptable to intimidate and harass environmentalists and other liberals.

He blamed statements by some elected officials. "The political majority ÷ the Republican Party ÷ has discovered a scapegoat in environmentalists," he said. "And they are riding that horse into the barn."