President Bush today urged Americans to "open their hearts and their wallets" to help victims of Hurricane Katrina, as he launched a private fund-raising effort led by former presidents Bill Clinton and George H.W. Bush.

Flanked by the two former presidents -- one his predecessor and the other his father -- Bush also appealed for patience with the federal relief effort in the face of growing frustration among stranded New Orleans residents pleading for food, water and transportation out of the flooded city.

He said National Guard troops are flowing into New Orleans to help maintain law and order, and he announced new measures to deal with disruptions in fuel supplies in the face of surging gasoline prices.

Bush's assurances came as Congress prepared to reconvene from its August recess to pass emergency legislation to fund relief efforts for victims of Katrina, which has displaced hundreds of thousands of people and caused billions of dollars in damage along the Gulf Coast from New Orleans to Mobile, Ala. Congress normally reconvenes after Labor Day. The Senate returns tonight and the House reconvenes Friday, congressional leaders said. Bush reportedly will ask lawmakers to approve $10.5 billion in emergency funding.

Homeland Security Secretary Michael Chertoff announced, meanwhile, that rescue and evacuation operations were continuing despite what he called "isolated incidents of criminality."

Amid rampant looting and signs of increasing chaos as stranded residents wait to taken out of New Orleans, thousands of National Guard troops under state authority are being deployed to the New Orleans area and Mississippi.

"Everyone is confident of the ability to maintain order," Chertoff told a news conference. He said that in addition to 2,800 National Guard troops now in New Orleans, 4,200 more -- or 1,400 a day -- would arrive over the next three days.

"The National Guard . . . will be deploying into the New Orleans area a force the size of the New Orleans Police Department each day . . . for the next three days," said Assistant Defense Secretary Paul McHale.

Lt. Gen. Steve Blum, chief of the National Guard Bureau, said the additional troops are "trained professionals" who serve as military police, and that many of them are "badge-carrying law enforcement officers" in civilian life.

"This is not, as it has been erroneously reported, martial law," Blum said. "This is helping a police force that is overstretched." He added, "Before it is over, you will see National Guard soldiers and airmen . . . from every state and territory in our nation responding to this national catastrophe." The deployments send the message that "when you call out the National Guard, you call out America."

Chertoff said there were "understandable crowd-control issues" at the Superdome in New Orleans, where buses sent by the Federal Emergency Management Agency and the Louisiana state government are evacuating thousands of refugees who were unable or unwilling to heed a mandatory evacuation order issued Sunday.

"The Superdome is secure," Chertoff said. He said a National Guard soldier suffered a leg wound in a shooting incident yesterday at the Superdome and that the perpetrator was arrested.

So far, about 1,500 "special needs people" who required medical attention and 2,000 other refugees have been evacuated from the Superdome to medical facilities and to the Astrodome in Houston, Chertoff said.

The mayor of San Antonio, Tex., Phil Hardberger, announced that the Alamodome in his city would also take in refugees, relieving some of the pressure on the 40-year-old Astrodome.

In a separate news briefing in Washington, the Army Corps of Engineers said one major breach in the New Orleans levee system would be repaired by the end of today, but that a second would take longer to fix. Once the gaps in the canal floodwalls are closed, the corps can begin working to pump out the floodwaters that have inundated about 80 percent of New Orleans.

The commander of the corps, Lt. Gen. Carl Strock, told reporters that a breach in the 17th Street Canal floodwall should be closed by tonight. However, engineers have not been able to get necessary equipment and material into position yet to plug a breach in the Industrial Canal.

Chertoff said he had no estimate of the fatalities from the hurricane and resultant flooding. But he said "hundreds of thousands of people" have been dislocated, creating a challenge similar to some that have occurred in disasters overseas and that have brought generous responses from the United States.

He said Canada, Germany and Britain were among "dozens of countries" that have offered assistance, offers that the White House said would be taken up and are being coordinated through the State Department.

In his appearance at the White House with his father and former president Clinton, Bush said his administration is "working with energy companies to repair and reactivate major refineries and pipelines" that have been disrupted by Katrina. He suggested that the disruptions could cause shortages and further price increases, despite loans of crude oil from the Strategic Petroleum Reserve and nationwide waivers on fuel blends.

"The good folks must understand that major refineries have been shut down, which means it's going to be hard to get gasoline to some markets," Bush said.

He said Colonial Pipeline, the major pipeline delivering refined products to the East Coast, "is back in operation, but only at 50 percent capacity."

"We're going to have a temporary disruption of gasoline product," he said.

Bush said he has instructed Chertoff to waive a legal requirement restricting shipping between U.S. ports to only American ships, so that "foreign ships can also help distribute oil and gasoline to where it's needed."

"This recovery is going to be a long process," Bush said. "It's also going to require a lot of money. And the federal government will do its part. But the private sector needs to do its part, as well. And that's why I've asked presidents Bush and Clinton to lead a nationwide fundraising effort to help the victims of Hurricane Katrina."

He said the former presidents "will ask Americans to open their hearts and their wallets to help those in need" in the days ahead, taking their appeals to large corporations, small businesses and individual citizens across the country.

The White House hopes they can duplicate their performance following last year's devastating tsunami in Asia, when they helped bring in millions of dollars in private relief contributions. All told, Americans contributed about $1 billion to the tsunami relief effort, the White House said.