Security measures put in place in the Metro and other local transit systems after Thursday's bombings in London will remain for the time being, even in the absence of information about any direct threats, transportation officials said yesterday.

Metro chief executive Richard A. White said 400 transit officers continued working 12-hour shifts patrolling the region's largest rail and bus system yesterday. Sixteen bomb-sniffing dogs and several heavily armed two-officer special response teams were conducting regular sweeps of rail stations.

Metro workers were handing passengers small cards to promote the system's "See it? Say it!" campaign, urging passengers to look out for unattended packages and suspicious behavior and to alert Metro personnel or police.

A spokesman for Virginia Railway Express said police forces from Washington to Fredericksburg were patrolling tracks and stations. Maryland Transportation Secretary Robert L. Flanagan said customers on MARC trains should expect to see increased police presence for at least as long as the national threat level remains at Code Orange for mass transit systems.

"We're urging the public to understand it has become an antisocial act to leave an unattended package anywhere in a public location, including on a subway, bus or train," he said.

Metro ridership was affected slightly, dipping Thursday to about 715,000 from a recent midweek average of 750,000, managers said. White said that commuter traffic was steady but that some discretionary or tourist trips were down. Yesterday morning's rush hour count of 204,067 riders was slightly above the same period last week, before the Fourth of July holiday, but down about 2 percent from two weeks ago.

Commuters heading home yesterday had a business-as-usual attitude. "Every day, you take a chance on everything you do. I just put faith in God," said Bobbi Poe, 59, a data entry operator, as she sat on a Red Line train on her way home to Landover. "I haven't even considered not taking the train."

Asked about recent security efforts, Poe said: "I don't think there are too many ways they can make it safer. People bring a lot of bags on the train, and they don't know what people are carrying."

Darryl Fagin, 63, a lobbyist who lives in Bethesda and has a daughter in London, did not give a second thought to changing his work routine. "I'm not going to change my life," he said as he stood on the platform at Farragut North.

Tourism officials said that travelers have somberly adapted to the possibility of terrorism and predicted that few would cancel trips.

Organizers of several large conventions planned for coming days confirmed that their events will go on as scheduled. The Academy of General Dentistry, for instance, will host 2,000 dentists from the United States and Canada at a conference next week. Spokeswoman Susan Urbanczyk said the group had not heard from any members concerned about safety.

The group sent an e-mail to conference attendees, directing them to information on security and asking them to submit emergency contact information to the group, just in case.

Local authorities acknowledged that the success of the bombers in London, one of the most security-conscious cities in the world, meant similar attacks could happen anywhere.

"Terrorists go to soft targets," White said. "What we need to do is create the impression that the transit system is prepared and protected and is not a soft target. That is really what all the experts say."

D.C. Mayor Anthony A. Williams (D) took to Metrorail yesterday to reassure riders. Wearing a white polo shirt, blazer, khakis and a navy blue Washington Nationals baseball cap, Williams posed with transit workers and urged the Bush administration and Congress to increase funding to secure public transportation.

"Our public transit system is safe. It is a vital part of our city, a foundation of our city," Williams told reporters after boarding an Orange Line train at Foggy Bottom at 10:47 a.m. and stepping off five minutes later at Metro Center. "We have to stand up to terror and the senseless feeling of victimization."

Thursday's bombings revived concerns raised by transit and rail industry officials after the Madrid commuter train bombings in March 2004.

Homeland security officials deferred industry requests for $6 billion in security aid but accelerated testing of baggage screening technology and announced creation of rapid-response teams of bomb-sniffing dogs.

"At the federal level, I don't think a whole lot has changed," White said, noting that although mass transit carries 32 million people per day, 16 times the passenger load of commercial aviation, the United States has spent $18 billion on aviation security and $250 million on transit.

White said Metro would like money to expand the number of buses with video surveillance cameras, now 100 out of 1,450.

It is also seeking money to expand a chemical detection system in place at about half of the 47 underground stations, add intrusion detection systems to stations and build a backup operations center.

Staff writers D'Vera Cohn and Nia-Malika Henderson contributed to this report.

D.C. Mayor Anthony Williams rides the Metro to reassure riders that the system is safe, saying, "We have to stand up to terror and the senseless feeling of victimization." He called for more federal funding for transit security.