Federal regulators are investigating whether Google’s recent changes to its main Web site are stifling competition by giving the company’s services preference in search results, according to a person familiar with the matter.

The Federal Trade Commission, expanding an existing antitrust probe, now will look at Google’s decision to incorporate data from its social network, Google+, into search results, said the person who spoke on the condition of anonymity because the probe is private.

Earlier this week Google said it would use contacts, posts and pictures from Google+ to provide what it described as a more personalized search. Users would automatically see that content after they enter search terms, but can opt out of the service by changing their search settings.

The change sparked criticism that the firm, which handles nearly seven in 10 search queries, is giving greater preference to its own social network over competitors such as Facebook and Twitter.

Similar concerns have been voiced by competing travel sites and consumer groups who say the company uses its unique status as a gateway for Web users to promote its own maps, travel, video and other services. Google has emerged as the biggest high-tech antitrust target since antitrust officials went after Microsoft in the late 1990s.

“Nothing would be off the table,” the person said about the investigation.

Google defended the change to its search engine, saying it is meant to help distill information on the Internet and make that data more personally relevant. If a user types “Martin Luther King Day” into the search engine, she will see fairly high up what her contacts on Google+ have said about the holiday.

“The laws are designed to help consumers benefit from innovation, not to help competitors,” Google spokesman Adam Kovacevich said. “We believe that our improvements to search will benefit consumers by better surfacing social content, and the great thing about the openness of the Internet is that if users don’t like our service, they can easily switch to another site.”

Other firms have incorporated social-networking features into search. Microsoft blends some data from Facebook into its results on Bing. Twitter, which has been critical of Google’s move, last summer ended a contract with Google to highlight its microblogging service in search results.