Google is set to begin helping customers buy advertisements in 50 U.S. newspapers in a test of how the Web search leader can extend its business into offline media, the company said on Sunday. Google said it has invited more than 100 advertisers already buying ads through its Web marketing system to join a three-month test of a Print Ads service that places ads in daily papers including the New York Times and Washington Post.

If the trial is successful, Google could extend the program to hundreds of thousands of its online advertising customers, offering newspapers a broad new sales channel that could help offset an ongoing decline in classified print advertising.

A year ago, Google, of Mountain View, California, began an earlier test in which it started selling print advertising in a handful of magazines, including PC Magazine. However, demand for the service was slow to take off, executives said in May.

In effect, Google is giving greater control over how ad sales are made. Advertisers log into the Google AdWords system and select newspapers and available ad space, then upload the advertising artwork. But newspaper publishers retain creative and financial control over whether to approve or reject bids.

The advertisements will appear in 50 metropolitan newspapers, including the Boston Globe, Seattle Times, the Philadelphia Inquirer and Chicago Tribune, along with papers in the Gannett Co. Inc. newspaper chain, a Google spokesman said.

Print advertising joins efforts by Google to expand into radio and video ads, allowing it to move beyond its Web-search marketing business that delivers pay-per-click text ads on its own site and others and accounts for the bulk of its revenue.

Google already offers click-to-play video ads through Web sites in its ad affiliate network. It has said it plans to start a public test of its Google Audio Ads that brokers ads on radio stations by the end of this year.

During the test program, Google's services will be free, but it plans on taking a sales commission eventually.