President Bush said Friday the power outages across the Northeast and Midwest are "a wake-up call" to the antiquated state of the nation's electrical grid (search) and urged those whose power has returned not to overload the still-limping system.

During a tour of a national park north of Los Angeles, thousands of miles away from the problem, Bush said it remained unclear what caused the massive blackout.

"It's going to take a while, I think" Bush told reporters. "But we will find out what caused the blackout, and we'll deal with it."

The president said the blackout will require changes in the country's electrical infrastructure.

"I view it as a wake-up call," Bush said. "I think this is an indication of the fact that we need to modernize the electricity grid ... make the electricity system have the redundancy necessary so that if there is an outage, like there has been throughout our history, that it doesn't affect as many people as it did in the past."

He said the wide-ranging energy bill he has tried to push through Congress has provisions that would help address the problem.

"Obviously something like this isn't going to happen overnight, but it begins to address the problem that this particular incident has made abundantly clear to the American people, that we've got an antiquated system," he said.

He urged patience from those affected by the power outages. "I think it's going to take a while to get 100 percent of the power up and running," he said.

Bush also asked that those whose power has come back on to think carefully about how much they need to use.

"It's important for our citizens who have got electricity in the Northeast and the Midwest to be wise about how they use the electricity," the president said. "They must conserve, because the more conservation there is now, the more likely it is their neighbor is going to end up having electricity in a quicker fashion."

As for direct federal assistance to state and local governments, Bush said it was so far limited to a request by New York City for the Pentagon to supply a generator. Health and Human Services Director Tommy Thompson has been calling hospitals to see if they need anything and Homeland Security Director Tom Ridge (search) has been working the phones as well, Bush said.

"This is a national problem and the federal government has got a responsibility to help local and state officials," Bush said.

Earlier, the president had talked by phone with Treasury Secretary John Snow, who told him the stock markets were up and running with only a few, minor glitches, White House press secretary Scott McClellan said.

Later, in a speech to park officials and volunteers at the Santa Monica Mountains National Recreation Area (search), Bush praised local officials and individuals for their handling of the crisis.

"The people of New York City and New York state and people of the Northeast and Midwest who were affected by last night's blackout kept their calm, were decent to their neighbors, really showed the rest of the country and the world the true character of the American people," he said. "I want to thank all of them for how they dealt with a very difficult situation and assure them that federal, state and local authorities are working hard to get the power up and running, take care of the needs of the people."