Key House and Senate committees yesterday approved bills to extend for two years a federal program that provides a backstop for private insurance companies in the event of another 9/11-style terrorist attack.

The measures would prevent the Terrorism Risk Insurance Act (TRIA) from expiring at the end of the year, but the bills contain a number of differences that must be worked out in the waning days of the congressional session.

The version approved by the House Financial Services Committee contains several provisions that the Treasury Department opposes, such as the addition of group life insurance and the kinds of coverage eligible for the backstop. The bill also calls for different triggers for different types of coverage -- a provision dubbed siloing -- that critics say would lower the damage level at which the federal program could be invoked.

The Senate bill increases the portion of losses insurers would have to pay and eliminates certain lines of coverage from the program.

Under the Senate measure, the amount of overall loss that triggers a federal payment would rise to $50 million in 2006 and $100 million in 2007. It is currently $5 million. The government's maximum liability would remain $100 billion.

An amendment to the House bill yesterday by Financial Services Committee Chairman Michael G. Oxley (R-Ohio) would boost the damage threshold by $50 million in each of the extension's two years.

The Treasury Department has not favored extension of TRIA, but agreed last summer to accept it if it were more restrictive than the original program and designed to be temporary, leaving coverage eventually to private insurers.

Treasury Secretary John W. Snow endorsed the version approved by the Senate Banking Committee. The panel's actions "recognize the temporary nature of the program and place terrorism insurance on the right path to full private market participation," he said.

The department is concerned that the House bill would "expand the program and increase risk to the taxpayers," spokeswoman Brookly McLaughlin said.

An extension of the government backstop is backed by a wide coalition of business groups, including not only insurers, but also builders, lenders, real estate investors and others who fear that lending and building would slow if developers are not able to get insurance for their projects.

It was backed in Congress by members of both parties, particularly those from urban areas that have been or might become terrorist targets.

"I do not regard TRIA as a favor to the insurance industry," said Rep. Barney Frank (D-Mass.). "It's a favor to the insureds."

The Treasury Department and other critics say the private market is now able to resume insuring against terrorism but will not do so as long as the federal government provides the coverage at little or no cost.

J. Robert Hunter, director of insurance for the Consumer Federation of America, said the House bill "would harm both taxpayers and consumers."

The bill "does not reduce taxpayer exposure to terrorism losses as much as the Senate bill and appears to actually increase taxpayer payments for larger terrorist attacks" by having the program pay for 95 percent of all losses above $40 billion, instead of the 90 percent called for in current law, Hunter said.