DENVER -- Several international banks have refused to provide Denver International Airport with a letter of credit backing $52 million in bonds, in part because of the shaky financial state of United Airlines, its largest carrier, officials said.

If United files for bankruptcy, it could cut payments to the airport said Debra Hinsvark, a spokeswoman for the city Revenue Department.

"They (banks) are all in such a wait-and-see attitude," Hinsvark said. "They want to see how United does."

The airport pays less than 2 percent interest on the bonds, and a letter of credit is required to keep that rate. If the airport can't renew the letter of credit, it may have to refinance the bonds at higher, fixed rates, which don't need a letter of credit.

Dexia Bank of Switzerland has agreed to extend the current letter of credit for three months but will not renew it, and the airport is negotiating with Bank of New York.