President Bush said Friday that Londoners shaken by a second wave of mass transit attacks in two weeks can count on the steadfast support of the United States.

"The people of Great Britain (search) must understand how strongly America stands with them during these trying times," Bush said in Atlanta during a speech on Social Security and Medicare. His audience responded with prolonged applause and a standing ovation.

"I'm confident, like our country, the citizens of that country will not be intimidated by thugs and assassins," the president said. "They understand what we know, they understand what the citizens of this country understand, is that we will hold true to our principles of human rights and human dignity and the freedom to worship."

"We're not going to let anybody frighten us from our great love of freedom," Bush said.

The president received several updates from his homeland security adviser, Fran Townsend (search), and planned a Saturday radio address focused on the London attacks. White House press secretary Scott McClellan said the United States would assist Britain "in any way we can" and had FBI officials working in cooperation with British officials.

No one was injured in the attempted bomb attacks Thursday on three subway trains and a double-decker bus in London. Still, British Prime Minister Tony Blair (search) said: "We can't minimize incidents such as this. They're done to scare people, to frighten them and make them worried."

The attacks followed a deadly series of explosions in London's subway and on a public bus two weeks ago. The alert level for U.S. mass transit systems was raised to orange at the time, and it was likely that would be prolonged as a result of the new bombings.

Homeland Security Secretary Michael Chertoff (search) and his staff discussed the mass transit alert levels several times Thursday, before and after the attacks, said two counterterror officials who spoke on condition of anonymity because of the sensitive nature of the information.

At the first meeting, senior national security officials were described as leaning toward dropping the transit system from orange, or high risk, back to yellow, signifying an elevated risk, although no final decision was made. By early afternoon Thursday, however, McClellan said, "There is no plan at this time to change the alert level for our mass transit systems."

Homeland Security Assistant Secretary Brian Besanceney said the department has reviewed the alert levels daily since they were raised to code orange on July 7.

"Certainly, as we look at the threat level, we will factor in the information and intelligence we're receiving from the U.K., as well as information we're getting from other sources, as we consider what the right protective measures are," he said.

The rest of the country remains at yellow alert, and counterterror officials said they have not seen any specific intelligence that would indicate an attack on the United States.

Maintaining security at orange alert levels — with increased police patrols, heightened inspection and surveillance and the use of bomb-sniffing dogs — costs mass transit systems an estimated $900,000 a day, said Greg Hull, security chief for the American Public Transportation Association (search).

Leaders on both sides of the Atlantic urged citizens to stand firm against attacks that they described as designed to scare people.

Bush said Friday that terrorists have "an ideology based on hate."

"They have designs, they have goals," he said. "They want to topple governments. They want us to retreat from the world so they can spread their idealogy of hate."

Some federal facilities stepped up their security measures, including the Pentagon, which is adjacent to a Washington-area subway stop, and the U.S. Embassy in London, which was temporarily closed to the public except for emergencies.

In Washington, subways and buses were running normally and authorities remained on heightened alert, Metro spokeswoman Lisa Farbstein said.

The London explosions triggered immediate reactions on Capitol Hill, where the House chaplain opened the day's proceedings with a prayer for any victims and one congressman called for additional funding for mass transit security.

"Instead of acting as a wake-up call, Congress seems to be hitting the snooze button," said Rep. Bob Menendez (search), D-N.J. "How many warnings do we need before we take action?"

But officials generally urged Americans to continue with their daily routines. Chertoff, for example, was keeping plans to leave Washington in the afternoon to meet with local officials Friday in St. Paul, Minn., a spokesman said.