Capitol Police Chief Terrance W. Gainer, challenging remarks by a top White House homeland security official, said yesterday that "there is not a specific, credible, direct threat against Congress as an institution, or its members."

Gainer was responding to statements by Frances Fragos Townsend, the White House homeland security adviser, who said in a television interview Sunday that the most recent intelligence on threats by al Qaeda included mention of the U.S. Capitol and members of Congress. Townsend said the information was not as detailed as it was for five financial institutions at the heart of the government's Aug. 1 decision to raise the terrorist threat alert for financial sectors in three cities.

Several other law enforcement officials in Washington said yesterday that they were not aware of any such information. Gainer, who has taken a series of aggressive steps to heighten security on Capitol Hill -- including a street closure and the addition of 14 vehicle checkpoints -- maintained, as he did last week, that he has no information indicating a current threat to the area.

"That said, we continue to be concerned about cells whose strategy, intent and planning targets the Capitol and all that it represents," Gainer said.

In recent weeks, the sergeants-at-arms for the House and the Senate have issued updated security warnings to lawmakers and their staffs in the wake of the latest terrorism alert.

According to congressional aides, House Sergeant-at-Arms Wilson "Bill" Livingood sent a memo to lawmakers urging them to take tunnels when walking from their offices to the Capitol for votes, remove license plates identifying them as members of Congress from their cars and take off congressional lapel pins when leaving the Capitol grounds. The warnings were first reported yesterday by Time magazine.

An aide to William H. Pickle, Livingood's Senate counterpart, said Pickle briefed senators in mid-July on security precautions and updated the warnings for senators and their chiefs of staff last week. The aide declined to discuss details of the briefings.

Gainer, who said Capitol Police have been issuing similar security warnings for the past 18 months, added that "encouraging members to be prudent not to draw attention to themselves is long-standing, good security guidance whose import takes on greater significance in these terrorist times."

Also yesterday, a Democratic senator contended that the disclosure of the identity of a captured al Qaeda suspect may have compromised national security and undermined an ongoing sting operation aimed at locating the terrorist network's operatives, including leader Osama bin Laden.

In letters to national security adviser Condoleezza Rice and Townsend, Sen. Charles E. Schumer (D-N.Y.) asked for an official explanation of why the suspect's name was leaked by administration sources and whether "this leak compromised future intelligence activity."

Schumer's objections followed widespread reports on the capture of Muhammad Naeem Noor Khan, whose arrest eventually led to the discovery of surveillance information targeting financial institutions in Washington, New York and Newark. The information was the primary basis for the government's decision Aug. 1 to raise the terror alert level for financial sectors in those three cities.

Khan, described as a computer expert for al Qaeda, became part of a sting operation organized by the CIA after he was captured last month. He sent coded e-mail messages to al Qaeda contacts around the world, according to U.S. officials.

In an appearance Sunday on CNN, Rice acknowledged that Khan's name had been given to reporters on background, meaning that journalists could not identify the officials who provided them with the information. Rice said officials were trying to balance "operational considerations" with providing the public with adequate information about the current terrorism threat.

Pakistani and British officials have been quoted in media reports as objecting to the identification of Khan. His cooperation had led them to other militants, including Eisa Hindi, an al Qaeda operative arrested last week in Britain who allegedly conducted much of the surveillance in New York.

Officials said yesterday that the FBI has warned U.S. law enforcement agencies nationwide that al Qaeda may try to use helicopters, limousines and rental storage facilities in an attack. The three classified bulletins, sent late last week, were prompted in part by clues unearthed in connection with the recent terrorism threat warning.

One or more pictures of helicopters were among hundreds of photographs and images seized from an al Qaeda operative's laptop computer, which also contained detailed notes from surveillance of financial institutions in those three cities, one law enforcement official said.

"Although there is no credible, specific evidence supporting the use of helicopters in aerial attacks within the United States, the threat cannot be discounted," the FBI said in one of the bulletins.

A separate directive issued last night said Transportation Security Administration screeners, or ones approved by the agency, must be used to check passengers and baggage on New York helicopters and that by tonight helicopter firms must provide information on their employees so background checks can be conducted.

The al Qaeda surveillance information also included the observation that a limousine packed with explosives would be more likely to pass through security at one of the potential targets, the Prudential Financial building in Newark, the law enforcement official said. The second FBI bulletin applied to rental vehicles in general, which were used in the 1993 bombing of the World Trade Center and in the 1995 Oklahoma City bombing.

The third bulletin urged police to monitor the use of rental storage facilities, which could be used to store explosives, weapons or other materials for use in a terrorist attack, the official said.

Staff writer Helen Dewar contributed to this report.

A police truck is parked outside the 30th Street heliport as a helicopter prepares to land in New York. Law enforcement agencies are being warned that al Qaeda might use helicopters in a terrorist attack. Sen. Charles E. Schumer (D-N.Y.) asked for an explanation of why administration sources leaked the name of an al Qaeda suspect captured in July.