Tribune said it will use some AP material such as sports statistics and stories it considers vital. The Chicago-based company said it is trying to determine whether severing ties with the news cooperative next fall is a viable option.

The company's television stations and newspapers' online editions will not participate in the experiment. Tribune also owns 23 TV stations, The Baltimore Sun and other dailies.

Newspapers' print editions will rely on Tribune staff and several other news sources including Reuters, The New York Times and GlobalPost. Not all the sources are normally available to Tribune papers, according to the company.

Telephone and e-mail messages seeking comment were left late Monday for Tribune Co. spokesman Gary Weitman and Chicago Tribune spokeswoman Kate Mersman.

"The Associated Press has been working with all members of the cooperative, including Tribune Co., to ensure that the AP news report retains its value to member newspapers and their readers," AP spokesman Paul Colford said in a statement to the company.

Last year, Tribune Co. gave the AP a two-year warning that it might drop the service, effective Oct. 15, 2010. Tribune Co. said at the time that it was keeping its options open while weighing what role AP would play in its future.

As of AP's annual meeting in April, about 180 newspapers - 14 percent of the AP's U.S. newspaper membership - had threatened to leave the news service. Reasons varied, but many complaints centered on cost.

The AP Board of Directors in April announced a new US$35 million in rate reductions for 2010 for its member newspapers on top of US$30 million in rate reductions for 2009. The AP expected the total assessment decreases for papers would average just less than 20 percent, but will vary widely depending on what content newspapers buy.

Tribune filed for bankruptcy protection in December because of dwindling advertising revenues and a crushing debt load of US$13 billion. Much of that debt was amassed when real estate mogul Sam Zell took the company private in 2007.

Tribune properties across the country have undergone cost cuts, including layoffs.