New York ? No one can know for sure whether an al-Qaida loyalist had what it took to follow through on a suspected plot to bomb Hudson River train tunnels. He had no explosives and no detailed plan, and isn’t believed to have visited New York, authorities said.

But U.S. officials said they weren’t willing to find out.

“We don’t wait until someone has lit the fuse (to) step in and prevent something from happening. That would be playing games with peoples’ lives,” Homeland Security Secretary Michael Chertoff said Friday as Assem Hammoud’s arrest in Lebanon was being announced.

Policy makers and security experts said the bust illustrates a shift in U.S. counterterrorism policy that has played out in other recent high-profile cases, including the arrest of seven men suspected of wanting to bomb Chicago’s Sears Tower.

Law enforcers, they said, are now willing to act swiftly against al-Qaida sympathizers, even if it means grabbing wannabe terrorists whose plots may be only pipe dreams.

“Before 9-11, the FBI was thinking in terms of criminal convictions,” said Rep. Peter King, chairman of the House Homeland Security Committee.

That meant waiting to act until investigators had hard evidence of a major crime, the New York Republican said. These days, he said, the priority is disruption.

“You may end up not winning it in court, but you get a bad guy off the street,” he said.

Authorities announced the arrests of Hammoud and two suspected accomplices on Friday.

FBI Assistant Director Mark J. Mershon called the suspects the “real deal,” but he described the suspected scheme as being in its earliest stages. The plotters only had talked about an attack, authorities said.

The announcement came two weeks after the arrest of an unconnected group of men in Miami and Georgia on charges that they were talking about blowing up skyscrapers in Chicago.

In that case, an FBI official described the group of mostly U.S. citizens as “more aspirational than operational,” with no explosives, funding or ties to established terrorist organizations.

The formative nature of the suspected plots prompted skepticism.

Joseph Cirincione, a national security analyst for the Center for American Progress, a liberal think tank, said he worried that the arrests of rather minor conspirators were being played up for political purposes.

“This is starting to look like the president’s version of rounding up the usual suspects,” he said. “There is a pattern of dramatic announcements, followed by revelations that these plots weren’t as serious as we all initially thought.”