"I don't know that we ought to apply the same strategy that we're using with the airlines," said Asa Hutchinson, undersecretary of Homeland Security. "Is it practical to have magnetometers for everyone who gets on a subway? Is it practical to search every bag that goes on?"
Asked by CBS News Early Show co-anchor René Syler whether he could reassure rail passengers they are safe, he replied, "I think they're aware that whenever we have a very open transit system, that it is difficult and challenging to have a 100-percent secure guarantee of safety. But we are working very hard to accomplish that."
Hutchinson, appearing on morning television news shows, sought to counter accusations by some congressional Democrats that the administration has not committed sufficient money to protection of the U.S. rail and transit systems.
"First of all, we've invested $115 million in grants to the transit and rail industry," Hutchinson said in one interview.
He said the federal government is working closely with state and local governments and added, "we've done a great deal of security and more needs to be done."
Security has been increased after the Madrid bombings, he said.
"We've increased law enforcement patrols. We have increased the presence of explosive detection teams. The public announcements alerting the thousands of passengers be on the alert for unattended bags," he said on The Early Show. "These are the types of things, as well as some additional measures that I would not want to talk about."
The government's alert status currently is at yellow, or elevated, the midlevel spot on the five-stage terror alert warning.
"We do have historic reporting that there are threats to mass transit systems," Hutchinson said. "But the current threat reporting does not justify any increase in threat level."
The British government said Monday it has had more police patrols in the London underground since late last year, but only decided to tell the public now, to try to make everyone more vigilant, reports CBS News Correspondent Steve Holt.