NYC raises security after transit threat

NEW YORK -- Authorities stepped up security yesterday after receiving what city officials called a credible threat that the New York subway could be the target of a terrorist attack in coming days. But Homeland Security officials in Washington downplayed the threat, saying it was of ''doubtful credibility."

The threat involved the possibility that terrorists would pack a baby stroller with explosives, among other potential subway bombing methods, a law enforcement official said, speaking on condition of anonymity because the investigation is ongoing. The official said the information resulted from the arrest of Al Qaeda operatives in Iraq.

New York officials mobilized police to begin looking through commuters' strollers, bags, briefcases, and luggage.

Mayor Michael Bloomberg called it the most specific terrorist threat officials had received to date. No one in New York had been detained, he said during a nationally televised news conference alongside Police Commissioner Raymond Kelly. ''We have never had before a specific threat to our subway system," Bloomberg said, adding that he still felt secure enough to take the subway home last night. ''Its importance was enhanced above the normal level by the detail that was available to us from intelligence sources."

The law enforcement official who spoke on condition of anonymity said the threat was ''specific to place, time, and method," which was a bombing. But US Homeland Security Department spokesman Russ Knocke de-emphasized the threat. ''The intelligence community has concluded this information to be of doubtful credibility," he said.

A counterterror official, briefed about the threat by Homeland Security authorities, said the intelligence was considered doubtful because it did not reflect ''on-the-ground, detailed" information. Rather, the official, who also insisted on anonymity, said the intelligence was similar to ''what can be found on the Internet and a map of New York City."

The law enforcement official in New York said city officials had known about the threat at least since Monday, but held the information until two or three Al Qaeda operatives were arrested in Iraq. Once the arrests were made, officials felt they could go public, said the official.

Authorities are concerned, the official said, that there might be Al Qaeda operatives in New York City connected to the plot. The official said authorities have no hard evidence yet of such a connection.

The US military spokesman's office in Baghdad had no information on the operatives' arrests. Pentagon spokesman Bryan Whitman said he had seen no indication of a US military operation to round up Al Qaeda suspects.

New York authorities said they wanted to leave nothing to chance in beefing up mass transit security. Governor George E. Pataki said the state would call up hundreds of National Guard troops and seek help from law officers in Connecticut and New Jersey to patrol commuter trains.

Because the threat appears specific to New York City, the MBTA Transit Police decided yesterday evening to keep the security measures the same for Boston's system, said Massachusetts Bay Transportation Authority spokesman Joe Pesaturo. The MBTA will continue to monitor the situation, he said.

Lucas Wall of the Globe staff contributed to this report.