Google’s efforts to track users across services such as YouTube and Gmail do not meet European standards of privacy, officials plan to announce Tuesday, in the latest of a growing number of regulatory challenges for the American technology giant.

A letter signed by regulators from more than 20 countries will call on Google to give users more notice about how their data is collected and seek consent in some cases, say people who have seen the letter. The company merged the privacy policies of 60 of its services this year, making it easier to track the behavior of its users but sparking concerns that it was amassing too much personal information.

Tuesday’s action comes as regulators in the United States and Europe prepare for the possibility of major antitrust cases against the company. Competitors such as Apple, meanwhile, are pressing claims of patent violations against several makers of devices that run Google’s Android operating system.

Taken together, the proliferating legal issues amount to a threat to the growth of one of the world’s most successful companies, which this month passed Microsoft as the second-most highly valued technology company, behind only Apple. Google stock is up 30 percent since July but has faltered in recent days.

“It’s never had this much government scrutiny coming at them at the same time,” said Danny Sullivan, editor in chief of the Web site Search Engine Land, which covers the search engine business. “They are big, and many people do worry about things that are getting bigger and seemingly unstoppable.”

Regulators worldwide have sharpened scrutiny of Google as the company has moved beyond its core search business and into electronic commerce, telecommunications, social media, online videos and more. A growing number of aggrieved competitors have complained to government officials, much as rivals to Microsoft did in the 1990s, setting up what proved to be an epic showdown between the U.S. government and the company.

That case, and a similar one in Europe, centered on allegations that Microsoft used the dominance of its operating system to benefit other products, such as its Internet Explorer browser. The antitrust allegations against Google carry an echo of that case; rivals accuse the company of using its dominance of the search market to help its moves into electronic commerce, travel and other businesses.

“They’re trying to build a moat around the castle and put alligators in the moat,” said Gary L. Reback, a Silicon Valley lawyer who represented a key Microsoft competitor in the 1990s and Google rivals now.

Google officials declined to comment Monday on the privacy case in Europe or the antitrust investigations. But Google officials have made clear their desire to avoid costly, distracting legal fights such as the ones waged by Microsoft.

“Twenty years ago, a large technology firm was setting the world on fire,” Google Executive Chairman Eric Schmidt said in Senate testimony last year. “Its software was on nearly every computer. Its name was synonymous with innovation. But that company lost sight of what mattered. Then Washington stepped in.