SAN FRANCISCO » Google is adding a new entree to its menu: free restaurant ratings from the Zagat review service.

Zagat, which Google bought in September, was charging $25 annually or $5 monthly for online access to its survey of diners. Those diners have rated about 35,000 restaurants in more than 100 cities around the world.

The reviews will be available for free on Zagat.com as well as several services on Google’s website as part of a change announced Wednesday.

"Now, the world’s highest-quality reviews are available to more people, whether they are at their desks or on the go," Zagat founders Nina and Tim Zagat wrote Wednesday on their Google Plus social-networking page.

Zagat will still charge $10 a year for using an application designed for Apple Inc.’s iPhone and iPad, although Google indicated it may eventually drop that fee. After a six-month free trial, Zagat charges $25 annually to see reviews on its app for mobile devices running on Google’s Android software.

The Internet fees helped protect sales of the burgundy-colored guides that Zagat has been putting out since its 1979 inception. For now, Zagat still intends to publish the guides, which were listed Wednesday on Amazon for $8.75 to $16.

Google Inc. acquired Zagat for $151 million in September to compete against Yelp’s popular online rating service. Google and Yelp Inc. are battling to attract more traffic to spur more sales of ads to neighborhood merchants.

Yelp explored a possible sale to Google for a reported $500 million in 2009 before deciding to go its own way. The two companies have since become prickly rivals, driven by Yelp’s allegations that Google rigs its search results to favor its own services over its competitors.

The Federal Trade Commission is looking into the complaints lodged against Google by Yelp and other Internet companies as part of a broad antitrust investigation.

The decision to turn Zagat into a free online service comes as part of Google’s expanded local business listings in its search results and the Plus service. The overhaul is being billed as "Google Plus Local" as the company continues to promote a social networking alternative to Facebook’s popular online hangout.

A search request for a restaurant that has been reviewed by Zagat will now trigger a listing that includes a breakdown of the service’s ratings. Zagat’s scoring system provides separate ratings on a 30-point scale for the quality of food, decor and service in a restaurant.

The new business listings, which will also appear on Google’s online mapping service and mobile device applications, will also include any pertinent recommendations from within a user’s contacts on Plus.