The Federal Emergency Management Agency has hired some of the nation's largest construction and engineering firms to provide temporary housing to Gulf Coast residents displaced by Hurricane Katrina.

The work, valued by two of the firms at up to $100 million each, will be performed under "emergency contracts" designed to "address the extreme housing needs of the region and the more than one million people who were forced to flee their homes because of the storm," according to a FEMA statement. "While not all evacuees will require housing, currently 163,000 citizens of Louisiana are now residing in shelters."

FEMA spokesman James McIntyre said that in the three affected states -- Alabama, Louisiana and Mississippi -- the agency estimates that 300,000 housing units will be needed. Some have already been built, including 300 in Alabama. McIntyre said there was no bidding for the contracts. Several of the companies already had contracts with FEMA. "We're familiar with their work, and they're large enough to get it done," McIntyre said.

The contractors have begun to look for sites, scouting state parks, recreational vehicle parks, Boy Scout camps and open fields in areas unaffected by the storm, company officials said.

The companies plan to provide people whose homes are uninhabitable with furnished, manufactured housing until they can either move back into their old homes or find new ones.

"We are working fast and furious to get these temporary housing units into place," said Lee C. Tashjian, a spokesman for Fluor Corp. of Aliso Viejo, Calif., one of the five companies chosen for the work. "But it's going to take some time."

The other companies selected to do the work are Shaw Group Inc. of Baton Rouge, Bechtel National Inc. of San Francisco, CH2M Hill Inc. of Denver and Dewberry Technologies Inc. of Fairfax.

FEMA already has in place eight contracts valued around $150 million for companies to provide manufactured homes and "travel trailers" in emergencies.

Bechtel did not have such a contract with FEMA, according to company spokesman Howard Menaker. He said the company started doing the temporary-housing work under a "multimillion-dollar letter agreement."

Menaker said the scope of the work and the value of the agreement are not settled, but that Bechtel has begun work in Mississippi. "We're working on short-term needs," he said. "It's reasonable to assume we'll be working on long-term needs as well. But right now, the concern is getting temporary housing in place."