Insurers are alert to the possibility that some claims filed after the deadly Sept. 11 attacks might be fake, and that certain ones may take slightly longer to settle, an industry trade group said on Monday.

"Companies will be vigilant in spotting and prosecuting insurance fraud," said John Eager, the National Association of Independent Insurers' (NAII) senior director of claims services. "Claims for some damaged or destroyed cars may be held up until authorities in the holding areas where demolished autos are being taken can match the vehicle identification numbers with the claims submission."

Insurers worldwide are expected to pay out $30 billion to $40 billion for damages resulting from hijacked planes' slamming into the World Trade Center and the Pentagon. This would be their biggest loss of all time, twice the size of Hurricane Andrew in 1992.

U.S. insurers have said they are working to expedite life and property claims after the attacks, in which thousands of people were killed. They plan to check for fraud later, they said.

But they are not ignoring the chance for fraud, NAII said. Insurance fraud already costs consumers almost $30 billion a year, or an extra $300 in insurance premium from every American household, it said.

"Insurers will carefully investigate questionable claims and work with law enforcement agencies to arrest these scam artists," Eager said.

Companies will cross-check information in the electronic database used by the Federal Emergency Management Agency, other disaster assistance agencies and insurers to detect duplicate or phony applications, Eager said. This could create some short-term inconveniences for policy holders, he said.

Crooks can create phony business receipts and file a business interruption claim, pretending they dealt with a firm operating in the World Trade Center, NAII said. Car fraud specialists may submit losses for damaged or destroyed cars that, in fact, were not in lower Manhattan during the attack.

Workers compensation insurers also are looking closely at "mental anguish" claims from witnesses to the tragedy who allege to be suffering from post-traumatic stress disorder after watching the twin towers collapse on television.

Insurers also will remain vigilant for claims from building contractors, cleaning workers and other emergency service firms for repair work that wasn't done, contents that were not damaged or lost personal property that never existed, they said.

Among other potential fraud scenerios, criminals might pose as professionals offering services to help displaced businesses lease space and relocate, and ask for money in advance.