TRENTON - Calls to the state's counterterrorism tip line more than doubled in the week after authorities foiled what they said was a plot to massacre soldiers at Fort Dix.

The tip line received 65 calls from May 8-14, the week beginning the day after authorities arrested six men they believed were conspiring to kill military personnel at the post. The 65 tips phoned in to authorities that week were more than twice the 30 calls to the tip line May 1-7, the week before the alleged plot was uncovered.

"We run them all down," Homeland Security and Preparedness Director Richard Canas said. "The ones that have merit get referred to the FBI."

It was just such a tip - from vigilant store clerks - that led to arrests in the Fort Dix case. The FBI said it learned of the young Muslims who are accused of plotting the massacre after workers from a Circuit City store became alarmed at the content of a video one of the suspects brought in for duplication in January 2006.

The government says the men, all foreign born but longtime residents of Philadelphia and its suburbs, had a weapons-training session in the Poconos and were trying to buy arms to carry out the attack.

Five of the six could face life in prison if convicted; the other suspect faces up to 10 years. All six are being held without bail. Lawyers for the men say they will plead not guilty.

The free tip line (1-866-4-SAFE-NJ) began early in 2003 as part of stepped-up antiterrorism efforts after the Sept. 11 attacks on the World Trade Center and the Pentagon. Before that, local and county police officers fielded many of the calls regarding suspicious activity, Homeland Security spokesman Roger Shatzkin said.

The tip line is manned around the clock by Homeland Security and Preparedness employees, who are mostly former law enforcement officers or military personnel. They are specially trained to do on-the-spot risk assessments based on information gleaned from callers.

Calls run the gamut of suspicious behavior, Shatzkin said: large groups of people in one house, comings and goings at night, vehicles with out-of-state license plates showing up on weekdays, people moving big boxes or duffel bags in and out of apartments or houses, and people seen videotaping sites along the New Jersey Turnpike, bridges or tunnels.

All legitimate tips are forwarded to the FBI's Joint Terrorism Task Force in Newark or Philadelphia for review. About half are quickly found to have no merit, Shatzkin said. An additional 25 percent or so are returned to Homeland Security or to county or local authorities for further checking, and the FBI investigates the rest.

Authorities would not say what percentage of tips panned out, but they say phone lines get busier after a terrorist attack and when a planned attack is thwarted. "An incident like the one at Fort Dix gets people's attention," Shatzkin said. "In this instance, it was such a strong example of a tip having a positive effect."