ST. LOUIS - Preparing for a catastrophic earthquake along the New Madrid fault is a priority, a FEMA official said Friday before a congressional field hearing on government readiness to handle natural disasters.

"New Madrid is at the top of the list," Michel Pawlowski, section chief of the Federal Emergency Management Agency, said. "It's our primary objective."

Pawlowski told a congressional committee that FEMA has "significant concerns" for the potential of a catastrophic earthquake equal in magnitude to those that struck parts of the Mississippi River Valley in 1811-1812, and again in 1895.

The estimated magnitude of those earthquakes is 7.5 or 8. The probability of a magnitude 6 or larger earthquake is 25 percent to 50 percent over the next 50 years.

Even a magnitude 7 earthquake would destroy more than 60 percent of buildings in St. Louis and Memphis, Tenn., because most buildings predate building requirements aimed at resisting the shock, officials estimate.

"A catastrophic earthquake in the central United States along the New Madrid Seismic Zone could pose unprecedented problems and challenges," Pawlowski said.

FEMA officials are worried about how quickly they could enter the affected area because many roads, bridges, and approaches could not be expected to withstand a high-magnitude earthquake, he said.

"It will be a monumental challenge," Pawlowski said. "That's why we want as many partners as possible to address this."

FEMA, which was sharply criticized for its handling of the aftermath of Hurricane Katrina, began in earnest in December to prepare for the possibility of an earthquake along the New Madrid fault.

Pawlowski would not say whether the Katrina criticism had prompted the agency's interest in the 50-mile-wide New Madrid fault zone, centered near the southeast Missouri town of New Madrid, and which stretches from Alabama to Illinois.

Instead, he pointed to its potential, wide-ranging impact on the nation's economy, estimated in the tens of billions of dollars.

He said a strong earthquake could disrupt the flow of commodities by underground pipeline, rail, barge and highway; halt the flow of food exports, fuel oil and coal outside the region; cripple FedEx's hub in Memphis, Tenn.; and block routes for emergency services.

Pawlowski said FEMA expects to have a regional response plan in place by June 2007.

A House subcommittee chaired by Rep. Bill Shuster, R-Pa., and which oversees FEMA and emergency management, traveled to Los Angeles on Thursday and St. Louis on Friday to gauge how prepared local, state and federal governments would be in responding to a natural disaster, and avoid problems that emerged with Katrina.

Shuster served on a special committee that last week released the findings of its investigation into the government's response to Katrina. Shuster said Friday he is leaning toward introducing legislation that would separate FEMA from the Homeland Security Department.

That's in response to criticisms that FEMA's traditional role of dealing in natural disasters has gotten lost in Homeland Security's emphasis on fighting terrorism.

"Response was slow and key decisions were made late," Shuster said. "We can't afford to get it wrong again. Business as usual doesn't work in a catastrophic disaster."

Missouri emergency management director Ronald Reynolds said most federal emergency funds have been tied to terrorism and not available for natural disasters. "That's been changing since Katrina," he said. "It's about time."

Eugene Schweig of the U.S. Geological Survey testified Friday that the 1800s New Madrid earthquakes and its thousands of aftershocks upended land, made the river unnavigable, and created landslides in a multistate region.

Such an event today would rupture underground pipelines, burst levees, and wreak havoc in the Midwest and East.

Sen. Jim Talent, R-Mo., and Rep. Jo Ann Emerson, R-Mo., have asked the federal government to conduct an emergency response exercise along the entire New Madrid fault zone to expose how response might be improved in the event of a devastating earthquake.