Four nonprofit groups devoted to investigative journalism will have their work distributed by The Associated Press, The A.P. will announce on Saturday, greatly expanding their potential audience and helping newspapers fill the gap left by their own shrinking resources.

Starting on July 1, the A.P. will deliver work by the Center for Public Integrity, the Investigative Reporting Workshop at American University, the Center for Investigative Reporting, and ProPublica to the 1,500 American newspapers that are A.P. members, which will be free to publish the material.

The A.P. called the arrangement a six-month experiment that could later be broadened to include other investigative nonprofits, and to serve its nonmember clients, which include broadcast and Internet outlets.