The $19.5 billion sale of the radio broadcaster Clear Channel Communications to two private equity firms is in jeopardy.

This time, however, instead of the buyers balking, the banks that had agreed to finance the deal have become apprehensive. Clear Channel and the private equity buyers may go to court to try to force the banks to complete the buyout, according to people briefed on the negotiations, who were given anonymity because they were not authorized to discuss the deal.

The legal threat is the latest indication that the banks have become reluctant to put up the money for the sale, these people said. Earlier, the banks proposed that the buyers  Bain Capital and Thomas H. Lee Partners  put down more cash and agree to stricter repayment terms. The buyout firms have refused.

Among the lenders are Citigroup, Deutsche Bank, Morgan Stanley, Credit Suisse, the Royal Bank of Scotland and Wachovia.