The former White House counterterrorism tsar, Richard Clarke, says the random search by police of bags on New York subways is a program that should be copied in other cities.

Terrorists who plan attacks with multiple bombs set to go off at the same time rely on knowing they will not encounter surprises by police that might derail their plans, Mr. Clarke said in a deposition for a federal court case challenging the search program.

“They rehearse that, they train it, they do dry runs,” Clarke said in response to questions posed by the New York Civil Liberties Union Legal director, Christopher Dunn. He said he believes most American mass transit systems are underprotected.

Mr. Clarke, a counterterrorism adviser to Presidents Reagan, Bush, and Clinton, has written a book strongly criticizing the current administration for underestimating warnings about Al Qaeda before the September 11, 2001, attacks.

The NYCLU has challenged the random searches which began in July, on the grounds that they violate the constitutional right of people not to be subjected to unreasonable search and seizure. Mr. Dunn says the searches are useless because they are performed at few stations, permitting people to evade them and enter the subway system elsewhere.

Mr. Clarke, though, said he found them “highly desirable” because they create the potential to surprise a terrorist. “They don’t want to be in a situation where one of their bombs doesn’t go off, because on the day that they chose to go in subway station X, there were police doing searches,” he said. “The presence of the program itself is the most important thing.”

He said he recently told key legislators from 36 states a series of specific things they could do to enhance homeland security, including instituting a random passenger search on any subway or light rail system. Mr. Clarke said he reached the conclusion after analyzing intelligence and other information about the jihadist network and looking at case studies of their operations.

“It’s on the basis of that kind of expertise that I’ve come to the conclusion that it is possible to deter jihadist terrorists, and to have them go to some other city or to some other target,” he said.

Mr. Clarke suggested that he played a key role in bringing about the program in New York, saying he spoke with one of the New York police officials who created the program on the day that subways were bombed in London in early July. He said he suggested the police institute random searches during the Republican National Convention in August 2004, although that was not done.

He also said he advised the mayor of Baltimore and the police commissioner there several weeks ago that they should institute a similar program.

There are about 19 subway or light rail systems in America, Mr. Clarke said.

Besides New York, he said Boston and Atlanta had occasionally tried similar searches during similar events.

“I’m not aware of any other American city that’s doing it on a regular basis yet, although I know many are thinking about it,” he said.