In a move that is certain to sharpen its rivalry with Facebook, Google (GOOG) on Tuesday is introducing a revamped version of its ubiquitous search engine that will dive deeply into the company’s fledgling social network, Google+, to find content that is relevant to a particular user. The change will expose Google+ profiles, as well as posts and photographs uploaded to the network, to hundreds of millions of search users whether or not they have Google+ accounts. In many cases, the changes will push content from other sites, including Facebook, further down on the search results pages.

Google said the changes were among the most significant it had made in years. “This is the biggest expansion of the kind of content that user can see since Universal Search,” Ben Gomes, a Google Fellow, said in an interview. Google introduced Universal Search, which began combining Web pages with images, videos and other types of content in search results, in 2007.

Starting Tuesday, a search for the name of a friend, for example, will likely bring that person’s Google+ profile as the top search result. As a result, their profiles on Facebook or LinkedIn will appear lower.

The changes are likely to renew persistent criticism that Google promotes content from its own services, like maps, reviews, YouTube and, now, Google+ ahead of those of rivals. Gomes said that Google is simply trying to make its search engine more useful. “Our goal is to bring the user the most relevant data based on their query,” he said.

Under the changes — dubbed “search, plus your world” — Google will also include in search results private content that a user has uploaded or that someone has shared with them on Google+ or Picasa. For example, if you search for Hawaii, you are likely to see pictures of your trip to Hawaii from your own albums, or from a friend’s album. You may also see travel tips and recommendations that your friends may have posted on Google+.

Generic searches for broad topics will now also include profiles and pages from Google+ for people who are relevant and important to that topic. A search for “music” may suggest the profiles of Britney Spears or Snoop Dogg to the right of search results.

This kind of personalization has long seen as a holy grail of Web search. Facebook has been working with Microsoft (MSFT) to allow that company’s search engine, Bing, to surface more personalized content. And the Facebook platform has allowed countless services, like Yelp, Pandora (P) and Spotify, to become more personal by showing users content that is relevant to their Facebook friends.

Users who do not want personalized content will be able to turn it off easily, the company said.