Security outside the White House closed down Pennsylvania Avenue near Lafayette Park. Yellow tape was put up to prevent tourists from getting close to the White House fence. (Marvin Joseph/The Washington Post)

The Secret Service expanded the security perimeter around the White House. Police beefed up shifts. Metro posted uniformed officers at busy stations during rush hour. Across the Washington region, public safety agencies reacted to the deadly bomb blasts in Boston by increasing efforts to keep the area safe.

“We’d be foolish to sit back and watch and say: ‘That’s Boston. Nothing for us to worry about,’ ” Montgomery County Police Chief J. Thomas Manger said.

With its plethora of public events, government buildings and large infrastructure systems, Washington is a target-rich area. But it is also well-trained in security preparations, with more than a decade of experience since the Sept. 11, 2001, terrorist attacks pushed the region into a permanent state of alert.

Those attacks also gave the area resolve to carry on, as D.C. Mayor Vincent C. Gray (D) pledged to do by encouraging residents and visitors to take part in Tuesday’s Emancipation Day festivities, a celebration of Abraham Lincoln’s 1862 signing of the bill freeing the District’s slaves. A morning parade down Pennsylvania Avenue NW followed by a gospel concert and fireworks show will go on as scheduled, Gray said.

“We hope people will continue to come down and continue to engage in this important celebration,” he said.

Public safety officials were quick to assure the public that security was being beefed up mostly as a precaution. They stressed that they had not received any information about specific threats to the area.

Visitors will see a “visible increase” in police presence in the District, said Metropolitan Police Chief Cathy L. Lanier. “We have a lot of assets and a lot of resources here, and everything that needs to be in place is in place,” she said.

The same was true with Metro.

Metro Transit Police were on heightened alert, said Metro spokesman Dan Stessel, and day-shift workers extended their duties into the evening rush hour. He said Metro spends millions of dollars a year on security cameras, bomb-sniffing dogs, chemical-detection devices and other anti-terrorism measures. The transit system’s newly appointed police chief, Ron Pavlik, said in an interview this month that he was considering increasing the frequency of bag checks for riders.

“We are operating the nation’s second-largest subway system in the capital of the United States. It should not surprise anyone that we are viewed as a potential target,” Stessel said.

Some police officials said that, in the long run, Washington is safer than many other places. Alan Goldberg, a longtime police administrator in the area who now serves as Takoma Park police chief, cited two factors: the many federal and local law enforcement agencies in the area, and the fact that most residents are well aware of the risks because government buildings are targets.

“This area is a more hardened target than other places,” Goldberg said.

He said the best prevention is good intelligence — preventing bombs from going off. Bigger groups can be easier to stop, he said, because there are more people involved. He also urged the public to report suspicious activity to police. “The lone-wolf people are the ones you really have to worry about,” he said.

Myriad other agencies reported heightened security measures across the region:

●Amtrak held over day-shift officers for evening duty and beefed up checks of stations and tracks.

Prince George’s County police increased patrols near “critical infrastructures” such as FedEx Field and National Harbor, according to Lt. William Alexander.

●The Secret Service closed off the area immediately north of the White House “out of an abundance of caution,” according to spokesman Ed Donovan. The Pennsylvania Avenue promenade and parts of Lafayette Park were cordoned with yellow police tape.

Other agencies said they were monitoring the situation in Boston. Fairfax and Prince William county police officials said they weren’t planning to make any security changes.

“At this point, we are not anticipating making any operational changes, but that is a minute-to-minute decision,” said Officer Bud Walker, a Fairfax County police spokesman.

Virginia State Police also have not taken any steps to heighten security in the wake of the Boston explosions, spokeswoman Corinne Geller said.

Lori Aratani, Mike DeBonis, Dana Hedgpeth, Jennifer Jenkins, Jenna Johnson, Justin Jouvenal, Patricia Sullivan, Clarence Williams and Matt Zapotosky contributed to this report.