SAN ANTONIO— The proposed $19.5 billion buyout of radio station operator Clear Channel Communications Inc. is reportedly near collapse because the private equity firms leading the deal are having trouble nailing down a financing agreement with banks.

Shares of Clear Channel, the largest radio station operator in the United States, fell 21 percent in after-hours trading on Tuesday to $25.82 after dropping $1.89, or 5.5 percent, to end regular trading at $32.56.

That is well below the $39.20 per share the buyout firms offered Clear Channel shareholders.

The Wall Street Journal reported on its Web site Tuesday that the private equity firms leading the buyout were having difficulty reaching terms with the banks committed to financing the deal. The report cited unidentified people familiar with the matter.

The buyout deal, which has been plagued by delays since it was announced in November 2006, was scheduled to close March 31.

A person familiar with the situation told The Associated Press that the equity partners, led by Thomas H. Lee and Bain Capital Partners LLC, are prepared to fulfill their obligation to fund and close the deal.

Because the stock has been trading below the buyout value, the lenders face the prospect of lending far more than the current market value of the company at a time when banks are already nervous about making loans. Failure to make good on previous lending commitments, however, could subject the banks to lawsuits.

The deal was struck during the years of easy credit that preceded the current crunch that is pressuring the U.S. market. The Clear Channel buyout remains the largest pending buyout in the U.S., according to Dealogic PLC. In addition to its radio holdings, Clear Channel is a major billboard company with roughly 1 million signs worldwide.