As Gulf Coast residents take measure of the devastating impact of Hurricane Katrina, federal officials face a cleanup and restoration cost easily topping the nearly $7 billion price tag of the 1994 Northridge earthquake in California, the single most expensive U.S. disaster to date.

While estimates of the overall cost of dealing with the floods and other damage in New Orleans and a wide swath of the Gulf Coast vary dramatically, some experts say the combined public and private spending on Katrina could run into the tens of billions of dollars.

"This is going to be the most expensive natural disaster that's hit the United States in history," said Sen. Thad Cochran (R-Miss.), who intends to push for quick approval of an emergency spending bill by his Appropriations Committee.

Last year, Congress approved two bills totaling $13.6 billion to cover the cost of four hurricanes, according to a White House fact sheet. That included money for highway repairs, military base evacuations, coastal restoration, national park cleanup, wastewater treatment plant repairs, and the administrative costs of providing billions in low-interest loans to small businesses and farmers.

The bulk of the money -- $6.5 billion -- went to the Federal Emergency Management Agency for immediate help with food, housing, transportation and medical needs, and longer-term assistance such as rebuilding property and providing legal, tax and mental health counseling.

FEMA, which responds to natural disasters, had $2.5 billion in the bank when Katrina stormed up through the Gulf Coast, said Scott Milburn, spokesman at the Office of Management and Budget.

"I think it's fair to say this is going to be a record," said Michael Buckley, a deputy director at FEMA who helps oversee the flood insurance program.

About one of every five properties with federally backed flood insurance coverage -- about 1.3 million homes and businesses -- is located in an area swamped by Katrina. The toll of those claims is going to be "astonishing," Buckley said.

Yet, even with its record-smashing potential, Katrina's impact is not entirely surprising. Federal payments for weather-related disasters have grown dramatically in recent decades, especially for hurricanes and floods, as more and more construction takes place along the coasts. Often unnoticed, the financial impact has been huge, totaling more than $31 billion in the last dozen years, according to FEMA figures, and forcing government officials and Congress to borrow funds and issue emergency appropriations.

As more storms pile into the coasts, the number of federal disaster declarations has surged, from an average 13 per year in the 1950s to 52 per year so far this decade. Federal disaster spending also has soared, from an inflation-adjusted $340 million in the 1950s to more than $25 billion in the 1990s, a review of federal disaster spending records shows.

Hurricanes and coastal storms account for a growing share of the tab. Even excluding Katrina, hurricanes represent eight of the 10 most expensive natural disasters in history, ranked by FEMA relief payments. Five of the storms have made landfall since 2001, signaling a return to what many meteorologists believe is a busier and more damaging hurricane period than in recent decades.

Disasters also are growing more expensive. Federally backed flood claims totaled $2 billion last year, about double what FEMA pays in an average year, and the agency borrowed $300 million from the treasury to cover claims.

Under its public assistance program, FEMA pays most of the cost to state and local governments of rebuilding their damaged infrastructure -- more than $13 billion in the last decade. In addition to replacing and repairing government-owned highways and bridges, the agency pays for debris removal and overtime expenses for police and emergency workers. It helps repair hospitals and schools, and covers such smaller items as stop signs, traffic signals and public tennis courts.

Generally, FEMA covers 75 percent of the cost, with state and local governments splitting the rest. Attempts to increase the local share have been beaten back over the years by local government and members of Congress. Some critics contend that federal taxpayers are paying too high a price -- essentially subsidizing some local governments that under-insure their public property.

FEMA also administers the National Flood Insurance Program, which provides the bulk of the nation's flood policies. (Private insurers do not insure against flood damage, which they consider too risky. Losses from wind damage are covered by private policies and insurance pools set up by state governments and others). As of 2002, the agency had about 4.5 million policies in place covering more than $600 billion worth of property, much of it along the coast.

Claim payouts have averaged about $1 billion a year for the last decade, according to Buckley, who helps oversee the agency's mitigation division, which includes the flood program.

Ivan, a withering Category 3 hurricane that barreled across the Florida Panhandle last year and flooded thousands of homes, changed that. It generated 30,000 claims valued at $1.3 billion. Including the other three hurricanes that struck Florida in 2004, FEMA and the private insurers it works with paid out $2 billion.

But as bad as last year was, this year is likely to be far worse. Katrina caused extensive flooding from Miami, near where it crossed over into the Gulf of Mexico, and all along the Gulf Coast from Alabama to New Orleans.

"Last year was a record year. This is going to be much more than that," Buckley added. "I can't even imagine what it is going to be."

Researcher Madonna Lebling contributed to this report.