The troubled National Flood Insurance Program drew criticism about its shaky finances and its methodology for gauging flood risk at a Senate hearing Wednesday.

The comments came less than a day after the Senate voted to extend the current program for a year. The most recent authorization expires on Sept. 30.

Run by the Federal Emergency Management Agency, the flood insurance program provides coverage to 5.5 million families and businesses. In recent years, it has run up an $18.8 billion debt, largely due to claims paid for Hurricane Katrina.

That figure came up repeatedly during the two-hour session before the Banking Committee, as senators and witnesses said rates needed to rise to reflect actual risk.

"It isn't actuarially sound," said Senate Banking ranking member Richard Shelby. "And it isn't going to be actuarially sound unless we do substantial reforms."

FEMA's process for remapping flood zones came under fire from Sens. Charles Schumer, D-N.Y., and Dick Durbin, D-Ill., who appeared as a witness at the hearing. Schumer told stories of constituents whose areas "haven't seen floods in over a century" but who, as a result of FEMA revisions, found themselves suddenly subject to a federal mandate to purchase coverage.

Schumer and Durbin argued for a five-year moratorium on mandates that those living in newly implemented flood zones have to purchase coverage. A House bill passed in July contains a similar provision and would also boost coverage limits and raise premiums for structures built before 1975, which had received a subsidy in the program.

Stephen Ellis of Taxpayers for Common Sense countered that a moratorium and gradual phase-in of rates for newly included houses, as some have proposed, was no way to set the insurance program on the road to solvency. He defended FEMA's mapping and expressed concern that as flood-zone boundaries changed, politicians hearing from angry constituents would be tempted to meddle.

"Legislation doesn't alter geology," he said. "And what makes good politics doesn't make good insurance policy."

Sen. Roger Wicker, R-Miss., made the case as a hearing witness for the FEMA program to offer wind insurance on a "voluntary and actuarial basis." Many Katrina claims were denied on grounds that damage had not been caused by winds, which ordinary insurance policies cover, but by flooding.

Rep. Gene Taylor, D-Miss., sponsored similar legislation in the House, but the White House threatened a veto, and House Democratic leaders pulled the measure in July. The insurance industry had lobbied against Taylor's proposal, arguing that it would drive private carriers out of the market. Flood policies are written by private insurers, but the coverage is underwritten by the federal government.