Google said Tuesday it will follow the activities of users across e-mail, search, YouTube and other services, a shift in strategy that is expected to invite greater scrutiny of its privacy and competitive practices.

The information will enable Google to develop a fuller picture of how people use its growing empire of Web sites. Consumers will have no choice but to accept the changes.

The policy will take effect March 1 and will also impact Android mobile phone users, who are required to log in to Google accounts when they activate their phones.

The changes comes as Google is facing stiff competition for the sometimes fleeting attention of Web surfers. It recently disappointed investors for the first time in several quarters, failing last week to meet earnings predictions. Apple, in contrast, reported record earnings Tuesday, blowing past even the most optimistic expectations.

Google’s move appears to be aimed squarely at Apple and Facebook — titans of the tech industry that have been successful in keeping people within their ecosystem of products. Google, which makes money by selling targeted ads, is hoping to do the same by offering a Web experience tailored to personal tastes.

“If you’re signed in, we may combine information you’ve provided from one service with information from other services,” Alma Whitten, Google’s director of privacy, product and engineering wrote in a blog post.

“In short, we’ll treat you as a single user across all our products which will mean a simpler, more intuitive Google experience,” she said.

Google can track users when they sign into their accounts. It can also use cookies or find out where people are if they use a Google phone or its maps program. The company will now attempt to mix all of that information together into a single cauldron for each person.

For instance, a user who has watched YouTube videos of the Washington Wizards might suddenly see basketball ticket ads appear in his or her Gmail accounts.

That person may also be reminded of a business trip to Washington on Google Calendar and asked whether he or she wants to notify friends who live in the area, information Google would cull from online contacts or its social network Google+.

Google said it would notify its hundreds of millions of users of the change through an e-mail and on its main search site.

Privacy advocates say Google’s new policy may betray users who did not expect their information would be shared across different Web sites when they signed up for a single service, such as Gmail.

A user of Gmail, for instance, may send messages about a private meeting with a colleague and may not want the location of that meeting to be used in Google’s maps application or social network.

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