If there is one essential piece of legislation before this lame-duck session of Congress it is the federal terrorism insurance bill -- a measure that has been agreed upon by President Bush and a conference committee of House and Senate leaders. No area of insurance needs this legislation more than our nation's oldest social benefit program: workers' compensation.

For almost a century, workers' compensation has been the one certain, comprehensive safety net available to all workers and their families. It pays for medical care, replaces lost wages and pays death benefits whatever the cause of workplace injury or death -- even if terrorism is the cause. As a result of the attacks of Sept. 11, 2001, this system will pay more than $3 billion in benefits to the spouses and children of those who were injured or lost their lives.

It is conceivable that another attack or attacks could affect large numbers of Americans in their places of work. It is also conceivable that another attack could cost the system many times the $3 billion from 9/11. Victims and their families will need a strong workers' compensation system to rebuild and renew their lives. Today that system is at risk unless Congress acts.

Workers' compensation is unique insurance coverage in that by law it must cover acts of terrorism and war. This sets it apart from other business insurance, such as property insurance, which can and has excluded this coverage. Because of the new and continuing threat of terrorism, underwriters have avoided insuring workplaces with high concentrations of workers or those in high-profile locations. Where insurance is available, it is at significantly higher prices. This has produced one of the many dampers on U.S. economic recovery.

In the event of another terrorist attack or attacks, the system itself could be in peril. Insurance companies could be forced into insolvency, and ultimately the promise of the workers' compensation system -- prompt, full, fair payment of benefits -- could be jeopardized.

This risk to the system is not tolerable. The American worker and our economy need assurances that people will continue to have access to workers' compensation benefits in times of national emergency. The workers' compensation system needs a backstop -- a threshold at which the federal government would step in to provide the funds to ensure all claims are paid.

Such a backstop is included in the Terrorism Risk Insurance Act of 2002, now before Congress. The idea of a backstop is not unique. The federal government has in the past provided needed commitments to insurance in areas at risk for civil unrest or flooding and for crop insurance protection. Terrorism is a national challenge and must be dealt with on a national level, as only the federal government can do.

The need to be prepared for worst-case scenarios with a risk-sharing plan is broadly accepted. President Bush and congressional leaders of both parties have made passage of a public-private terrorism insurance plan -- in which insurance companies offer the first wave of financial protection and the government acts as a backstop -- a high priority. It would be a travesty if Congress failed to give final passage to this bill and thereby put the workers' compensation program, as well as other business insurance, at risk.

As with many pieces of major legislation, the bill has tradeoffs. But it achieves the fundamental purpose of protecting our economy and providing confidence that people can rebuild their lives in the wake of another terrorist incident.

Preventing another terrorist attack on our homeland is our nation's number one priority. But we must be realistic about our ability to defend against this menace. The unfortunate truth is that we can't possibly shield our nation against every conceivable threat. We can and must take steps to ensure that such a tragedy would not be compounded by economic ruin.

The writer is chairman, president and CEO of Liberty Mutual Group, a leading property and casualty insurer.