WASHINGTON - February 18, 2008 - Amtrak, the only long-haul passenger rail service in the United States, will for the first time randomly screen passengers' bags and deploy armed security officers on trains and platforms, the railroad said on Monday night.

Details of the shift in security strategy at Amtrak will be released on Tuesday, but the railroad said the steps were not in response to any threat.

Since the hijacked airline attacks on U.S. landmarks in 2001, the Madrid train bombings in 2004 and the London subway bombings a year later, Amtrak has tightened security for ticketing and boarding and employed other behind-the-scenes measures. Some of them are permanent, while others, like bomb-sniffing dogs, are used randomly.

But the overall response for rail security pales in comparison with the multibillion-dollar systems for screening passengers and their bags for bombs and weapons at U.S. airports.

Critics point to relatively easy access to trains and their infrastructure as a serious security vulnerability.

Amtrak previously considered other programs to screen passengers but rail and U.S. security officials often pointed to the difficulties of trying to secure a sprawling rail network that feeds into commuter and subway lines.

Amtrak alone carries more than 25 million people annually over a 21,000-mile (33,800-km) route system. Its heavily traveled flagship line runs from Boston to New York and Washington.

The U.S. Transportation Security Administration, which oversees airline and some rail security operations, said it supported Amtrak's new initiative.