In a speech billed as a progress report but sounding more like a call to arms, President Bush urged Americans to "be vigilant" and use their "eyes and ears to stop those who would do us harm."

"There is a difference between being alert and being intimidated, and this nation will never be intimidated," Bush said in a prime-time speech to about 5,000 service workers in Atlanta.

The assembled police officers, firefighters, military personnel, health care and postal workers all showed up to hear the president express his gratitude and stir their patriotism.

To them all, Bush offered his thanks, in particular singling out postal and health care workers who have faced another type of terror following the Sept. 11 attacks — an anthrax contamination that has killed four of the 17 people infected with the bacterium.

Calling the person or people who sent anthrax through the mail "uncivilized," the president said the bioterrorism attack has been narrowed down to three letters. Only one death, a New York City hospital worker, cannot be traced to the other infections.

"Tonight we come here to thank a whole new group of people who never enlisted to fight a war," Bush said. "I am proud of the way our health care and postal workers are responding with calm to this deadly threat."

With three dozen pauses for applause, the president received his most stirring ovation of the evening when he improvised a line expressing his pride in the military.

He added that the best way to defend the homeland is "to take the battle to the enemy and to stop them."

"We are destroying training camps, disrupting communications and dismantling air defenses ... we are deliberately and systematically hunting down these murderers and we will bring them to justice," he said.

Bush said the United States is at the beginning of its effort in Afghanistan and "Afghanistan is the beginning of our effort in the world."

America's enemies want to destroy freedom and impose their views, get rid of Jews and Christians and silence women, Bush said. He said America's only possible response to that kind of enemy is to stare it down and defeat it.

"Those who celebrate the murder of innocent men, women and children have no religion, have no conscience and have no mercy. We wage a war to save civilization itself. We did not seek it but we will fight it and we will prevail," he said.

The president asked Americans to enlist in the war on terror by showing the "true values of America through a million acts of common decency."

"We are a different country than we were on Sept. 10: sadder and less innocent; stronger and more united; and in the face of ongoing threats, determined and courageous," the president said.

He praised the public for pre-empting his "Communities of Character" initiative that he planned to introduce this fall to spark a rebirth of interest in service. He said the initiative has been replaced with a spontaneous outpouring.

"We are a nation awakened to service," Bush said. "Many ask what can I do to help in our fight? The simple answer is all of us can become a Sept. 11 volunteer by making a commitment to service in our own communities."

He offered several suggestions such as tutoring or mentoring a child, comforting the afflicted, housing the homeless, participating in neighborhood watches and crime stoppers, volunteering in hospitals, and supporting troops in the field by becoming active in the United Service Organizations.

The president said Americans abroad can act as "ambassadors of culture" and said he wants to encourage communication among children of the world through a letter-writing campaign.

"Ours is a great story and we must tell it through our words and through our deeds," he said.

The president also asked Americans to consider new opportunities in AmeriCorps and Senior Corps, domestic versions of the Peace Corps.

Bush said he is creating a task force to find ways to encourage more volunteerism and explore the creation of a "modern defense service to respond to local emergencies when the manpower of government is stretched thin."

"I call on all Americans to serve by bettering our communities and therefore defy and defeat the terrorists."

He said the United States government has done a lot to secure the nation by putting the National Guard at airports, adding air marshals to flights, stepping up border control, and tightening immigration controls but urged Congress to "put needless partisanship behind us" and look for ways to increase security, expand the economy and make the United States less dependent on foreign oil.

He asked Congress to "work hard and put a stimulus plan into law to help the American people" as well as send him an airport security bill that will make cockpits more secure, increase screening of luggage, and "put the government in charge of all airport screening and security."

The president on Friday will announce an expanded role for National Guard troops at airports, including putting them at boarding gates, administration officials said Thursday.

The announcement is expected during a White House ceremony honoring private-sector employers of National Guard and Reserve personnel.

The president said that Americans must also continue to focus on things that have not changed — faith, devotion to family, commitment to freedoms and principles — and to take inspiration from the people who didn't know they had signed on to be heroes, including the passengers of United Flight 93 who crashed their plane into the ground rather than let the terrorists hit a populated area. Among them was Todd Beemer, who led the passenger revolt and with whose last known words Bush signed off.

"We have our marching orders, my fellow Americans: 'Let's roll.'"

The Associated Press contributed to this report.