As his blue-and-white jet swooped low over New Orleans and the Gulf Coast, President Bush pressed his face against the window and stared out at oblivion.

He saw an expansive lake where a storied city used to be. He saw mile after mile of flattened houses turned into so many matchsticks. He saw highways that disappeared into water, a train plucked off its track, a causeway collapsed into rubble. And he saw the next daunting challenge to confront his presidency.

After a month-long retreat at his Texas ranch, Bush returned to Washington on Wednesday in crisis-management mode, where his administration is likely to remain indefinitely. With his poll numbers at an all-time low, Bush faces one of the stiffest leadership tests since Sept. 11, 2001, with continued violence in Iraq, gasoline prices topping $3 a gallon in many places and now what he called "one of the worst natural disasters in our nation's history."

In response, Bush mobilized one of the biggest relief efforts in history as his administration tapped the nation's oil reserves and dispatched Navy ships, medical teams, search and rescue squads, electrical generators, a mobile hospital, and millions of gallons of water to the region. Bush warned that it would take years to repair the damage, and aides said he expects to seek a special appropriation from Congress.

While critics accused Bush of being slow to recognize the horrible scale of the damage wrought by Hurricane Katrina on Monday, he moved Wednesday to reassert his public leadership role and reassure the American people that he is in charge. After his 35-minute flyover along the Gulf Coast, he raced back to Washington, met his disaster relief team in the White House and strode into the Rose Garden to address the nation.

"This is going to be a difficult road," Bush said, flanked by Cabinet secretaries, and he rattled off statistics to illustrate all the federal government is doing to help. "The challenges that we face on the ground are unprecedented. But there's no doubt in my mind we're going to succeed."

The words echoed the language Bush used through much of his August vacation whenever he emerged from the ranch to defend his handling of the Iraq war, and it reflected his leadership style. In times of calamity, he seeks to project an air of undiminished confidence regardless of the dark circumstances. He fashions himself a take-charge leader who thrives at making decisions that he never second-guesses even if they do not turn out the way he imagined them.

"The can-do stuff, relating to some physical or material problem, is something he can do -- he has strength there," said Fred I. Greenstein, a scholar at Princeton University who has long studied presidential leadership. "I think this a more natural thing for him than the other cerebral stuff."

But in a capital suffused with anger and partisan division, it did not take long for Bush's leadership on Katrina to come under question. Noting that it took Bush two days to cut short his vacation and return to Washington, Democrats painted the president as dithering while New Orleans drowned. "He has to get off his mountain bike and back to work," Rep. Rahm Emanuel (Ill.), chairman of the Democratic Congressional Campaign Committee, said in an interview.

Other Democrats began circulating accusations that the administration had neglected disaster preparedness to pay for the Iraq war and noting that National Guard units that usually respond to natural catastrophes have been fighting overseas.

"President Bush's wake-up call came awfully late," said Sen. Frank Lautenberg (D-N.J.). "We are watching this devastation unfold on our televisions for days, and you have to ask: Where is the federal government? The National Guard's first priority must always be to protect people at home."

In that way, the latest crisis facing Bush is already converging with the previous two. Democratic criticism will further inflame the debate on Iraq, just as U.S. forces there finish their third-deadliest month since the war began. And the disruption to the oil supply in the Gulf of Mexico could push gas prices so high it exacerbates public resentment or triggers economic turmoil.

"Our citizens must understand this storm has disrupted the capacity to make gasoline and to distribute gasoline," Bush cautioned in the Rose Garden, shortly after television pictures showed long lines at Atlanta gas stations charging as much as $5 per gallon.

But if Bush will be judged by his response in the weeks ahead, aides acknowledged that he is constrained by limited options. He decided Wednesday to tap the Strategic Petroleum Reserve, which could hold down the increase in gas prices marginally, but other than monitoring for price gouging, a senior White House official said, there is little else Bush can do.

The president has more levers to pull to help hurricane victims, and he is mindful of the lessons from his father's administration when it was criticized in 1992 for responding too slowly to Hurricane Andrew in Florida. Bush plans to visit the Gulf Coast on Friday or Saturday to inspect the damage.

The president used his trip back from Texas to get a sneak preview, observing the arc of devastation from aboard Air Force One en route to Washington. Col. Mark Tillman, the chief pilot, took the plane down from its cruising altitude of 29,000 feet and skimmed just 1,700 feet above the ground at one point.

"It's devastating," Bush told aides as he flew over New Orleans. "It's got to be doubly devastating on the ground."

From the air, New Orleans appeared almost completely washed out, with portions still submerged and virtually no cars on the roads that were still above water, a haunting view of a city with virtually no visible signs of habitation. Bush noticed the Superdome with part of the skin of its roof peeled back and saw a residential neighborhood where the water reached all the way up to, and even above, the roofs of houses. As Bush watched, a Coast Guard helicopter hovered so low that its rotor blades whipped up the water below; it appeared the helicopter might have been in the midst of a rescue.

Heading east to the city's outskirts and beyond, he saw that some suburban and rural communities were virtually obliterated. Acres and acres of forest were leveled, the trees flattened as if stepped on. An amusement park appeared to be a model in a bathtub, the roller coaster emerging from the water.

As he reached Mississippi, Bush saw the other most devastated area around the towns of Waveland and Pass Christian, where there was not much water but many miles of wooden houses smashed into scrap lumber as far as the eye could see. "It's totally wiped out," Bush said.

For long stretches of the coast, no building appeared to be standing, and those few that were showed signs of severe damage. The president pointed out a church still standing while all the houses around it were destroyed, White House spokesman Scott McClellan said. In Gulfport and Biloxi, casinos sat partially smashed.

"There wasn't a whole lot of conversation going on," McClellan said. "I think it's very sobering to see from the air. And I think at some points you're just kind of shaking your head in disbelief to see the destruction that has been done by the hurricane."

Staff writer Jim VandeHei in Washington contributed to this report.

From Air Force One, President Bush views the devastation left by Hurricane Katrina along the Gulf Coast.