After four days on high alert, police announced on Monday that they were scaling back security measures in the subways because no evidence had emerged that an alleged terrorist plot to blow up trains would be carried out.

Officials said they were still investigating claims by a federal intelligence agency informant that Al Qaeda operatives in Iraq had schemed to attack the subways using baby strollers and brief cases packed with remote-controlled explosives as early as Oct. 7. They also continued to defend a decision to flood the subways on Oct. 6 with thousands of extra police officers.

But the arrest and interrogation of three suspects by U.S. forces in Iraq had so far produced no information to corroborate a possible threat, authorities said.

"Things were moving in the right direction," Police Commissioner Raymond Kelly (search) told reporters at the Columbus Day Parade (search) in Manhattan. "We're going to slowly reduce our coverage to what it was pre-Oct. 6."

Kelly stressed that police would continue random bag searches and other precautions in the subways that were launched in the summer in response to the bombings of the London transit system (search).

John Miller, an assistant FBI director and the agency's chief spokesman, said federal authorities agreed with the police department's assessment that any potential risk had subsided.

Miller said the operation in Iraq "would have served to neutralize any threat that may or may not have existed."

The suspects in custody in Iraq denied they planned to coordinate with operatives who were already in the city to carry out an attack, said two law enforcement officials. The men had passed polygraph tests, the officials added.

"The people supposedly standing by in New York probably were never there," one of the officials. Both officials spoke on condition of anonymity because the investigation had not been completed.

Still, city officials stood by their decision to heighten subway security, saying the initial tip had come from an informant with a reputation for reliability, and was too specific to ignore.

"We did precisely the right thing," Kelly said. "We had no choice but to respond the way we did."