WASHINGTON -- Two days after Hurricane Katrina slammed into the Gulf Coast, the Department of Housing and Urban Development announced plans to issue emergency vouchers aimed at helping poor storm victims find new housing quickly by covering as much as $10,000 of their rent.

But the department suddenly backed away from the idea after White House aides met with senior HUD officials. Although emergency vouchers had been successfully used after the 1994 Northridge earthquake in Los Angeles, the administration focused instead on a plan for government-built trailer parks, an approach that even many Republicans say would concentrate poverty in the very fashion the government has long sought to avoid.

A similar struggle has occurred over how to provide health care to storm victims. White House officials are quietly working to derail a proposal by leading Republican and Democratic senators to temporarily expand the Medicaid program. Instead, they are pushing a narrower plan that would not commit the government to covering certain groups of evacuees.

As President Bush tackles the monumental task of easing the social problems wrought by Katrina, he is proving deeply reluctant about using some of the big-government tools at his disposal, apparently out of fear of permanently enlarging programs that he opposes or has sought to cut.

Instead of depending on long-running social programs for such services as housing and health care, the president has generally tried to create new, one-shot efforts that the administration apparently hopes will more easily disappear after the disaster passes. In practice, that has meant relying on the Federal Emergency Management Agency, which thus far has run virtually all of the recovery effort.

"FEMA can help fill some immediate needs after a disaster, like giving grants to help people repair their roofs or pay for temporary housing," said John P. Sucich, a former senior FEMA official, who oversaw the recovery from the 1989 Loma Prieta earthquake in the San Francisco Bay Area. "But it is not the agency to turn to to ensure the kinds of continuing help that families need to begin putting their lives back together.

"That's what the rest of government is for," Sucich said.

At least in the case of housing, critics say that the president's unwillingness to rely on existing programs could wind up raising costs. Instead of offering $10,000 vouchers, FEMA is paying an average of $16,000 for each trailer in the new housing parks it is contemplating. Even many Republicans wonder why the government would want to build trailer parks when many evacuees are now living in communities with plenty of vacant, privately owned apartments.

"The idea that in a community where we could place people in the private housing market to re-integrate them into society, we would put them in [trailer] ghettos with no jobs, no community, no future, strikes me as extraordinarily bad public policy, and violates every conservative principle that I'm aware of," said former House Speaker Newt Gingrich, a Republican.

"If they do it," Gingrich said of administration officials, "they will look back on it six months from now as the greatest disaster of this administration."

Defenders of the president's approach say that it will help Katrina's victims without sticking American taxpayers indefinitely with higher costs for social programs. "Once you begin to expand any entitlement, it's very hard to pull back," said Grace-Marie Turner, a health policy analyst with the conservative Galen Institute.

Turner raised particular concerns about the bipartisan Senate Medicaid plan, which would expand who could get coverage and require Washington to pay the full cost of the program, including amounts normally covered by states, for up to 10 months. If the plan were adopted, she said, "then every state that has reason to declare an emergency will want full federal funding for Medicaid as well. ... It would be very hard to say no."

The administration's hesitancy to rely on well-established social programs goes beyond housing and health care.

When White House officials realized the full dimensions of the hurricane disaster, one of the first actions they took was to announce that FEMA would provide storm victims with $2,000 cash grants. Originally, the money was supposed to have come in the form of debit cards, but when the agency proved unable to smoothly issue these, it switched to checks. But there has still been trouble, which some experts trace to the agency's -- and the administration's -- unwillingness to turn to the government's existing system for doling out aid.

"If FEMA had used the ... state welfare offices and unemployment agencies, they'd have been a lot better off," said William Waugh, a disaster specialist at Georgia State University and a board member of the national accreditation group for emergency managers.

"The agency was not designed, and has never been very good at anything but immediate emergency services," Waugh said. "It's been particularly bad at delivering continuing social services like cash assistance."

Some critics of the administration are calling on it to substantially expand the existing system of unemployment assistance to funnel money to people uprooted by the storm. In the past, extensions of unemployment benefits, once signed into law, have been difficult to end.

So far, the administration has been planning to give assistance almost exclusively through FEMA, which has the legal authority to distribute the substantial sum of $26,200 per household in cash, rental assistance and home repairs. If even half of families displaced by the storm collect, the agency could end up paying out tens of billions of dollars. But once the amounts were paid, that would be the end of the government's obligation.

In Medicaid, too, the White House is struggling to avoid setting any precedent that might permanently expand the program by negotiating state-by-state deals to cover storm victims rather than agreeing to uniform rules for covering them.

The administration is advancing the state-by-state approach as an alternative to a bipartisan proposal drawn up by Sens. Charles Grassley, R-Iowa, and Max Baucus, D-Mont., which has been endorsed by Senate leaders of both parties as well as other prominent Republicans.

That plan would expand Medicaid for poor storm victims uniformly in all states where they are now located, at a cost of as much as $8 billion over the next five months. It would open the program to some people not normally covered, such as childless adults of working age, and would require Washington to pay 100 percent of the cost of care instead of splitting the costs with the states, as it normally does.

By contrast, the administration approach generally would not expand coverage beyond people who were already eligible for Medicaid at the time of the hurricane.

Administration officials say that victims without other forms of health insurance would have to seek free care at hospital emergency rooms, a practice the government normally discourages because of the cost. The administration has promised to obtain more funding to compensate hospitals providing the free care.

The administration position has opened a growing fissure between Bush and other Republicans. On Wednesday, Mississippi Gov. Haley Barbour, a Republican who is usually supportive of the White House, declared that the Senate Medicaid plan "is what we need." Sen. Trent Lott, R-Miss., has also sided with the Senate plan over the White House.