SAN JOSE, Calif. — Extending a surge that began last year, Google Inc. says 2011 will be its largest hiring year ever, plans that would mean the Internet giant will add more than 6,000 new workers over the balance of this year.

With the hiring plans, Google will have more than 30,000 employees by the start of 2012, a workforce still significantly smaller than Silicon Valley giants like Intel Corp., Cisco Systems Inc. and Hewlett-Packard Co., but more than double the size of rivals like Yahoo Inc., and more than six times the size of the company that has become its most formidable competitor — Facebook Inc.

“”Obviously, we’re optimistic about the future,”” Google Senior Vice President Alan Eustace said in an interview Tuesday. “”The growth that we’re seeing across a lot of different areas is really based on seeds we planted a long time ago. We made investment decisions a long time ago to plant the seeds in different areas, and the exciting part is those seeds are actually developing now; those seeds are coming into fruition. I think it’s unusual for a company to see so many opportunities align.””

Among those major investments were Google’s $1.65 billion purchase of YouTube in 2006 and its $3.1 billion purchase of the display advertising network DoubleClick in 2007.

The surge reflects Google’s ambitious plans to become a powerful force in areas of the Internet far beyond its traditional sweet spot of Web search. The company is rapidly increasing the number of engineers working on initiatives such as its Android operating system for smart phones and tablets, its maps and location-based services that could deliver advertising to users based on their location, and in its Chrome browser and operating system areas.

“”It’ll be pretty much across the board,”” Eustace said of Google’s hiring plans.

While much of the hiring will happen in and around Google’s headquarters in Mountain View, Calif., the company also plans to add more than 1,000 workers in Europe, many of them in and around its hub in Munich, Germany, outgoing CEO Eric Schmidt said at a conference in Europe on Tuesday. Google now has over 60 offices in 30 countries.

About one-third of Google’s workforce is in the Sam Francisco Bay Area, and Eustace said the company’s 2011 hiring would be weighted at least in that ratio — meaning Google plans to hire at least 2,000 people in that area

Google last week reported fourth-quarter revenue of $8.44 billion, a 26 percent jump compared with the fourth quarter of 2009. Google notched profit of $2.54 billion, or $7.81 a share, a 29 percent jump over the same quarter in 2009.

Google added 4,565 workers in 2010, a 23 percent jump in its global workforce. It was the company’s biggest personnel expansion since 2007, Google’s biggest year for hiring, when the company added about 6,100 workers.

“”We had a fantastic 2010; we had a fantastic 2009, given the situation,”” Eustace said. “”I feel like given what we know now, the prudent decision is to actually expand.””

As Google continues to grow, incoming CEO Larry Page’s biggest challenge will be to recapture the nimbleness of a startup that characterized the company’s early days. While Google says two-thirds of the startup founders who joined Google through an acquisition are still with the company, some longtime employees who have left the search giant say a company of more than 20,000 people by its nature can’t move with the speed of a startup.