Passengers at the nation's airports will see more bomb-sniffing dogs and uniformed police on patrol as the Federal Aviation Administration ordered tighter security Friday for the first time since 1995.

Government buildings and military bases around the country also were battened down a bit tighter in the wake of U.S. missile attacks Thursday on suspected terrorist facilities in Afghanistan and Sudan and the expectation that the targeted groups may try to retaliate.The FAA cited information from law enforcement and intelligence agencies about new terrorism threats but cautioned that the new security measures do not reflect any specific threats at airports.

"These are prudent and precautionary steps to ensure the safety of travelers," said FAA spokesman Eliot Brenner.

Increased canine bomb-sniffing units and additional use of trace explosive detector units at security checkpoints are among the measures the agency is implementing. Curbside parking restrictions will be strictly enforced. And agency inspectors will be posted at airports in the United States and abroad to monitor security operations for domestic carriers.

Brenner said other measures are being taken "that travelers will not see."

The agency has cautioned airlines to be mindful of discriminatory practices and not to target passengers based on ethnicity or religious affiliations during screenings.

Many airports had already acted on their own. "As the events transpired, everybody kind of just gets a little bit higher up on their toes," said Benjamin Decosta, general manager at Hartsfield Atlanta International Airport.

Military bases around the country went to what is known as Threat Condition Alpha, the first of four levels of increased security instituted when there is a general threat of terrorist activity.

"We have a sharper eye on things," said Capt. Glen Roberts, a spokesman for the 437th Military Airlift Wing at the Charleston, S.C., Air Force Base. "If you see folks you don't recognize who don't look like they should be there, you challenge those people."

At Elmendorf Air Force Base near Anchorage, Alaska, officials began requiring that visitors who want to fish, hunt or golf on the base have a sponsor.

The Nuclear Regulatory Commission as a precaution advised operators of the nation's 110 atomic power plants and university research reactors to step up security but agency spokesman Victor Dricks emphasized that the NRC had received no credible threat to any nuclear facility.

In the nation's capital, tourists and commuters boarding subways were told over intercoms that a security alert was in effect and "not to leave unattended items in Metro-rail stations and trains" and to report any suspicious items, activities or persons.

Extra police and closer inspections of identification and packages greeted people entering government buildings and landmarks.

"We're not aware of any overt threats" against Americans at home or against national symbols, such as government buildings or the popular Washington monuments, FBI spokesman Bill Carter said Friday.

The FBI nonetheless issued a general security warning. "It is reasonable and prudent to conclude that yesterday's action by the United States elevates the risk to U.S. interests worldwide," the agency said in a statement.

The cruise missile attacks were both retaliation for the fatal bombings at two U.S. embassies in Africa two weeks ago and prevention against future terrorism, U.S. officials said.

"We have beefed up and we want to be seen as having a heavy presence," Pentagon spokesman Glenn Flood said. "This will continue until further notice."

Pentagon security guards searched workers and others with building passes who would ordinarily be passed through. Black-clad SWAT teams roamed the grounds with automatic weapons.

One extremely unhappy Marine Corps general got his Honda Accord stuck as he negotiated a temporary ramp at one entrance Friday morning. A red-faced security guard scrambled to get the general on his way.

At the State Department, cars and trucks were parked across the entrances to two driveways. The horseshoe-shaped drives were long ago closed to ordinary traffic as a precaution against car bombers but are usually blocked only by temporary metal barriers.

The uniformed division of the Secret Service added guards around various diplomatic missions.

The General Services Administration, which manages federal buildings nationwide, sent out an internal security advisory Thursday suggesting that guards step up patrols and more carefully check bags of anyone going inside, spokeswoman Eleni Martin said.