He also urged people whose power has been restored to conserve energy.
During a visit to the Santa Monica Mountains north of Los Angeles, Mr. Bush said it was still unclear what cause the massive blackout.
"It's going to take a while," Mr. Bush told reporters, urging patience from those affected by the power outages. He said he will order a review of why so many states were hit by a massive power blackout
The president also said the blackout will require changes in the country's electrical infrastructure.
"It's a wake-up call," Mr. Bush said. "The grid needs to be modernized, the delivery systems need to be modernized. We've got an antiquated system."
On Thursday night, Mr. Bush assured Americans that "this was not a terrorist act."
He credited local and state emergency officials with quickly getting a handle on the problem.
"We're better organized today to deal with an emergency than we were 2½ years ago," he told reporters at a San Diego hotel.
Mr. Bush, in California for a two-day campaign fund-raising swing, also said it "has been remarkable to watch on TV" how calmly individuals reacted.
Meanwhile, the administration's top energy official, Energy Secretary Spencer Abraham, was nowhere to be seen during the blackout crisis.
Abraham made no appearances and released no statements Thursday as the blackout darkened an area from Connecticut to Michigan, including New York City.
New Mexico Gov. Bill Richardson, the energy secretary under President Clinton, was all over the airwaves. Richardson blamed the blackout on the country's "Third World electricity grid."
It turns out Abraham was on a work-related trip in London. Energy Department spokeswoman Jeanne Lopatto said Abraham was scheduled to return to Washington by Friday afternoon.
In a statement released Friday morning, Abraham urged consumers in the affected areas to conserve energy and unplug major appliances until stable power is restored.
"Utility crews are working to restore the remaining service, to determine the cause of the outage and to take steps to ensure that such incidents do not occur in the future," he said.
Abraham has been in Europe all week. On Tuesday, he test drove a fuel cell vehicle at a DaimlerChrysler facility in Germany. He was in the Netherlands Wednesday, promising $3 million for radioactivity detectors in the busy port of Rotterdam.