Emergency measures by federal and local police were keeping tourists and residents in limbo. No visits to the Capitol. No tours of the White House. No posing at the Lincoln and Jefferson memorials. No flights from Reagan National Airport, just across the Potomac.

At dozens of streets leading to city landmarks, District of Columbia police and their federal counterparts blocked traffic, and Humvees remained stationed on various street corners.

It is a day-to-day decision about public access.

''People are scared. People are in crisis mode,'' said Maria Ramos, 25, of Washington. She organized a candlelight vigil in a largely immigrant neighborhood several blocks north of the White House. ''This feeling of security has been shattered.''

On Friday, members of Congress crossed town to join President Bush and other government officials at a prayer service at Washington National Cathedral. Security was tight.

''We're asking the public to remain patient,'' said Sgt. Rob McLean of the U.S. Park Police, which oversees the National Mall.

Added Terrance W. Gainer, Washington's deputy police chief: ''We have to be on guard and vigilant about the potential for further terrorist activities.''

Inside the White House's security zone were the collections of the Corcoran Gallery, the capital's oldest art museum.

''We want to open as soon as possible,'' said Jan Rothschild, spokeswoman for the private institution, whose art school will stay open. ''Art has a great power to heal. We want to be open so people can see the art work and get as much solace as they can.''

Dan Duncan, who works in the Maritime Trades Department of the AFL-CIO, one block north of the White House, said only pedestrians with government IDs were allowed into Lafayette Park, which is across Pennsylvania Avenue from the executive mansion.

The park usually is a popular spot for lunch-goers.

''I do realize the need for security, but you've lived in this town and you've worked here - you just never thought you'd see this happen,'' he said.

From the FBI to the Secret Service to the Washington force, police agencies kept a vigilant watch all week.

The Customs Service on Wednesday and Thursday flew P-3 surveillance planes, normally used to find drug boats in the Caribbean, to help the Defense Department spot suspicious aircraft, said a Customs official, speaking on condition of anonymity. On Friday, the planes were not flown but remained on standby, the official said.