COLORADO SPRINGS, Colo. — While insurers have more capacity to write some terrorism risks, the federal terrorism insurance backstop remains a vital part of the terrorism insurance framework, a panel of insurance executives said.

The prospect of renewing the Terrorism Risk Insurance Program Reauthorization Act of 2007 remains unclear, however, especially in the current climate of political gridlock, several of the panel members said Sunday.

To win reauthorization, the program may have to be modified, they said.

TRIPRA, which was the second renewal of the Terrorism Risk Insurance Act of 2002, remains an integral part of the terrorism insurance market, said F. Michael Crowley, president and co-chief operating officer of Markel Corp. in Glen Allan, Va. He was speaking during a panel session at the Insurance Leadership Forum in Colorado Springs, Colo., which is sponsored by the Council of Insurance Agents and Brokers.

“I don't think we are in a position to do without it,” Mr. Crowley said.

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Given the nature of the risk, it's appropriate that the government should be involved the insurance program, said Mike McGavick, CEO of XL Group P.L.C., “because terrorism succeeds when governments fail to protect their citizens.”

The main problem that insurers and reinsurers face when trying to underwrite terrorism risk is their inability to model the risk, said Nikolaus von Bomhard, chairman of the board of management at Munich Reinsurance Co.

While the severity of most terrorism risks can be estimated, the frequency cannot — and any terrorism risk involving biological or nuclear devices would be “impossible” to underwrite, he said.

The insurance industry does have the capacity to cover more terrorism risk than it does today, but prices for the portion of the risk that it can cover would increase significantly without the federal backstop in place, said Peter J. Eastwood, president of Berkshire Hathaway Specialty Insurance Group in Boston.

If the cost of terrorism insurance increased significantly, fewer policyholders would buy the coverage, which would be bad from a public policy standpoint, Mr. Eastwood said. However, to win support from a fractured Congress, it is likely the federal program would have to be modified, he said.

Renewing the program will be difficult, and the entire industry should get behind the effort, said Leigh Ann Pusey, president and CEO of the American Insurance Association, who moderated the discussion.

“I think we have a battle ahead of us,” she said.