Yahoo is expected to launch today a contextual advertising program - using an ad platform similar to Google's AdSense - for small-to-midsize web publishers, including blogs, report CNET and DM News. Yahoo has been working for months on a self-serve contextual ad service tailored to bloggers and other small online publishers, thus encroaching on what has been Google territory.

Yahoo and Google are already rivals in serving major search-advertising partners, but Google has held an effective monopoly on text ads for smaller sites, including blogs.

Yahoo will now include smaller websites in the Yahoo Publisher Network and will roll out the beta program to 2,000 publishers, and plans to expand it by yearend. Yahoo's Content Match contextual listings will allow publishers to place contextually relevant text ads on their web pages and split with Yahoo the revenue generated from the links.

Content Match will also allow publishers to distribute their content on Yahoo via RSS to drive traffic back to their sites.

Content Match will let publishers customize the ads that appear on their sites as well as display ads that are "consistent with the look and feel of their site," said Yahoo spokesperson Guade Paez.