With virtually the entire upper echelon of the government gathered under one roof, security precautions at the Capitol last night were the tightest in recent memory.

U.S. Capitol Police, who had warned members of Congress that the building would be the No. 1 target of any terrorist campaign linked to the war in the Persian Gulf, set up extra checkpoints, cordoned off the Capitol for several blocks in each direction, and put all of its 1,250 officers and bomb-sniffing dogs on duty.

"We're in a completely different atmosphere now," said Dan Nichols, a police spokesman. "I don't want it to appear that we're ever lax at any other time of the year, but I think it's fair to characterize this year as a bit more serious than usual."

"Our goal is to make it as hard as possible to come into the Capitol," House Sergeant at Arms Jack Russ said.

One Cabinet member could not show up. Interior Secretary Manuel Lujan Jr. was required to stay away as this year's official non-attendee, guaranteeing that in case of disaster, someone in the line of succession to the presidency -- he's No. 8 -- survives.

Russ said that people holding tickets to the House gallery for President Bush's State of the Union address would have to go through at least three security checkpoints, the last of which included a new machine that can detect some explosives.

The detector was put into operation yesterday morning at the south entrance to the Capitol. Russ said several of the machines were ordered six months ago, and eventually will be in place at all entrances to the Capitol, to be used in conjunction with the standard metal detecting X-ray machines in use. Russ said the sniffing machine is sensitive enough to pick up traces of firecrackers on clothing a week after being handled.

Since the outbreak of war with Iraq, police also have been requiring visitors to the Capitol to remove their coats for searches, in addition to the standard searches of briefcases, purses and the like.

In addition, members of the House and Senate have been given a series of security briefings in which they were advised to use the underground corridors linking their office buildings to the Capitol, remove markings identifying them as members of Congress from their vehicles, and briefed on how to recognize suspicious looking letters and packages.

"There's no sense in making things easy," Russ said.

For last night's speech, all streets within a four-block radius of the Capitol were closed, including Independence and Constitution avenues. Staff aides and news reporters who are usually allowed to park on the East Plaza of the Capitol were required to move their cars three hours before Bush's arrival at the Capitol.

Senators were given a specific time to march from their side of the Capitol to the House chamber for Bush's speech and told to walk in an orderly fashion.

Though many members of Congress were abiding by the new warnings, their cooperation was not without a price. John H. Chafee (R-R.I.) reluctantly removed from his car the license tag identifying him as a U.S. senator and said "the next day I got a parking ticket."

Staff writers Helen Dewar and Debbi Wilgoren contributed to this report.