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.

“It’s something we’ve talked about for a long time, since part of our mission is to enable our members to share material with each other,” said Sue Cross, a senior vice president of The A.P. She said the development in 2006 of an Internet-based system for members to receive A.P. material made it easier to do that kind of sharing, and to offer new products like the investigative service.