ASHINGTON, Sept. 11 — President Bush vowed tonight to retaliate against those responsible for today's attacks on New York and Washington, declaring that he would "make no distinction between the terrorists who committed these acts and those who harbor them."

"These acts of mass murder were intended to frighten our nation into chaos and retreat, but they have failed," the president said in his first speech to the nation from the Oval Office. "Our country is strong. Terrorist acts can shake the foundation of our biggest buildings, but they cannot touch the foundation of America."

His speech came after a day of trauma that seems destined to define his presidency. Seeking to at once calm the nation and declare his determination to exact retribution, he told a country numbed by repeated scenes of carnage that "these acts shattered steel, but they cannot dent the steel of American resolve."

Mr. Bush spoke only hours after returning from a zigzag course across the country, as his Secret Service and military security teams moved him from Florida, where he woke up this morning expecting to press for his education bill, to command posts in Louisiana and Nebraska before it was determined the attacks had probably ended and he could safely return to the capital.

It was a sign of the catastrophic nature of the events that the White House kept his whereabouts secret during much of the day as he was shuttled about on Air Force One, with an escort of F-16's and F-15's.

Tonight, he looked tense and drawn, as he declared that "today our nation saw evil, the very worst of human nature."

"The search is under way for those who are behind these evil acts," Mr. Bush said. "I have directed the full resources of our intelligence and law enforcement communities to find those responsible and to bring them to justice."

His mention of the terrorists and the countries they operate from were the closest the White House would come to assigning blame for the attacks. Intelligence officials said they strongly believed that Osama bin Laden's terrorist organization was behind the attacks. But Afghanistan and administration officials insisted there was no hard evidence to connect Mr. bin Laden to today's attacks.

One of his national security officials said tonight, "I have never seen the president so angry or so determined."
Mr. Bush asked the country to pray tonight, for the thousands who are dead, "for the children whose worlds have been shattered, for all whose sense of safety and security has been threatened." He quoted from the 23rd Psalm: "Even though I walk through the valley of the shadow of death, I fear no evil, for you are with me."

The nation and the world closely watched the president's demeanor as they listened to his words tonight. This national moment was for him as much about tone and bearing and emotional projection as it was about the substance of his remarks. The coming days will require him to master the images of sturdy authority and presidential strength.

The president departed abruptly from an elementary school in Sarasota, Fla. More than 12 hours later he was back in the White House, the day's events having created a natural tension between security officials who wanted to whisk Mr. Bush to safety and the political desire to present him publicly as a leader firmly in charge at the White House. But Mr. Bush's security team said it was not safe to return to Washington earlier than this evening.

Mr. Bush, who staffers said was eager to return to the White House, seemed as shaken as the rest of the nation when he made a brief statement this morning at Barksdale Air Force Base near Shreveport, La., the first stop of Air Force One on the president's daylong odyssey. Leaving Florida, Air Force One took a zigzag course — east to the Atlantic, then north, then west — and then to Barksdale. It was unclear tonight why the jet took that course.

"Freedom itself was attacked this morning by a faceless coward," the president said. "And freedom will be defended." He added that "the full resources of the federal government" would help the victims of the attacks.

"Make no mistake, the United States will hunt down and punish those responsible for these cowardly acts," Mr. Bush said. Then he concluded: "The resolve of our great nation is being tested. But make no mistake: we will show the world that we will pass this test. God bless."

Shortly afterward, Mr. Bush reboarded his aircraft and flew to Offutt Air Force Base in Omaha, the command post of America's nuclear forces and one of the most secure military installations in the United States. There Mr. Bush led a meeting of the National Security Council by video phone to Washington with Vice President Dick Cheney and Condoleezza Rice, the president's national security adviser, who remained in a White House that had been evacuated earlier in the day.

But the president's political aides had to face a central question: How could Mr. Bush appear in control, and calm the nation, from a bunker in Nebraska? But they also were aware that if Mr. Bush returned too soon and was evacuated again, it would appear he was fleeing the capital. So White House officials waited until it seemed the attacks had ended, before allowing Mr. Bush to return to Washington.

Cameras tracked his movements as he flew by helicopter to the South Lawn of the White House, snapped a salute to his Marine One guard and walked across the lawn to the Oval Office. It was a journey rich in symbolism: one of Mr. Bush's advisers said it was critical to show that "the president was back in Washington and there there is a return to something like normality." Mr. Bush strode across the South Lawn at 7 p.m. and addressed the nation from the Oval Office at 8:30 p.m.

Ari Fleischer, the president's press secretary, said that it was Mr. Bush who made the decision that the hopscotching from one air base to another had to stop, and that it was time to head back to the White House. "The president wanted to get back to Washington," Mr. Fleischer said.

"He understood that there can be a period of caution so that the security people can make a full and proper assessment about any threats. They were afforded that opportunity. The president traveled to a secure location while they took that opportunity. And now, obviously, the president is returning home safely."

Republicans, who have worried for months whether Mr. Bush has been appearing sufficiently presidential, described the speech as the most important of his presidency and said it would be a test like no other Mr. Bush has faced.

Mr. Bush was informed that a plane had hit the World Trade Center in a telephone conversation with Ms. Rice shortly before walking into a second-grade classroom at the Emma E. Booker Elementary School in Sarasota, Fla. White House officials said he knew only that it was a single aircraft and not necessarily a terrorist attack. The president did not appear preoccupied until a few moments later, around 9:05 a.m., when his chief of staff, Andrew H. Card Jr., entered the room and whispered into the president's ear about the second plane attack. At that moment Mr. Bush's face became visibly tense and serious.

"This is a difficult time for America," Mr. Bush said. Air Force One departed from Sarasota at 9:55 a.m. Among those on board were Mr. Card; Karl Rove, Mr. Bush's senior adviser; Mr. Fleischer, and Dan Bartlett, the communications director. Once on the ground at Barksdale, the president's plane was surrounded by Air Force personnel in full combat gear with M-16's. William J. Bennett, a former education secretary under President Ronald Reagan and a drug czar under former President George Bush, the current president's father, said in an afternoon interview that it was important for Mr. Bush to return to the White House as soon as possible.

"This is not 1812," he said. "It cannot look as if the president has been run off, or it will look like we can't defend our most important institutions."