NEW YORK — The Sun-Times Media Group, owner of the Chicago Sun-Times and dozens of suburban newspapers, filed for bankruptcy reorganization Tuesday, making it the fifth U.S. newspaper publisher to seek protection from creditors in recent months.

The step, brought on by a precipitous decline in advertising revenue, means both of Chicago's major daily newspapers are operating under bankruptcy protection. Tribune Co., the parent company of the Chicago Tribune, the Los Angeles Times and other newspapers, filed for bankruptcty in December.

The Sun-Times Media Group, which filed in a Delaware court, said it will continue to operate its print and online properties. The company listed $479 million in assets and $801 million in debt.

It has retained Rothschild Inc. to help with a possible sale of assets.

"We firmly believe that filing for Chapter 11 protection and exploring the potential sale of assets or new investment in the company offers us the best opportunity to protect our respected media properties for the long-term," Jeremy Halbreich, the company's interim chief executive, said in a statement.

Chapter 11 bankruptcy frees a company from the threat of creditors' lawsuits while it reorganizes its finances. The debtor usually retains control of the business and its assets.

"We firmly believe that filing for Chapter 11 protection and exploring the potential sale of assets or new investment in the company offers us the best opportunity to protect our respected media properties for the long-term," Jeremy Halbreich, the company's interim chief executive, said in a statement.