NEW ORLEANS—The federal government says it will pay hotel expenses for some of the nearly 2 million people who fled their homes ahead of Hurricane Gustav, but exactly who will be eligible for assistance and how much it will cost taxpayers is uncertain.

Officials from the Federal Emergency Management Agency planned a telephone news conference Thursday night to answer questions about the plan.

Homeland Security Secretary Michael Chertoff said Wednesday in Baton Rouge that FEMA would pay hotel costs “to make sure that people don’t feel economic pressure to return home prematurely, before it’s safe.”

He said FEMA would pay hotels directly, so it was unclear whether those who had already paid for rooms and checked out would be eligible for reimbursement.

With two other hurricanes threatening the East Coast, the decision to pay for hotels could make it easier to evacuate residents during the next disaster. But doing so would also burden the agency with huge expenses.

The news that hotel costs might be reimbursed came too late for people who have been sleeping at public shelters, such as those in a convention center in Birmingham, Ala. Some of those evacuees said they would have preferred a hotel if they had known FEMA money would be available.

“You can just get cat naps here,” said Aaron Clark, 63, as he sat under a shade tree outside the center. “We didn’t get breakfast this morning because they said something was broke down. It’s just surviving, that’s all it is.”

FEMA officials in Louisiana urged residents affected by the storm to register with the agency and to save receipts that document their spending during the evacuation.

“We’d need receipts, and we’d need to know whether the area they were evacuated from is one of the mandatory evacuation areas,” said Ed Conley, a FEMA spokesman.

Conley was asked, as an example, whether a family could be reimbursed for hotel expenses after leaving New Orleans on Sunday, checking into a Tennessee hotel, then returning after two, three or four nights.

“That’s exactly the family we want to get in touch with us,” Conley said.

But he was uncertain what the agency would offer such a family, in part because various other factors—including the family’s insurance coverage and whether their house was damaged—could come into play.

Also, the minimum number of days that would be covered had not been determined, and it was unclear whether food and fuel costs incurred while on the road would be covered.