MOUNTAIN VIEW, Calif. - In the latest sign of its ambitious growth plans, Google Inc. has signed a 40-year lease to secure space for a huge office complex that will be built on a federal government research center near the Internet search leader's Silicon Valley headquarters. The 1.2 million-square-foot campus announced Wednesday fulfills a vision that Google first laid out with the NASA Ames Research Center in 2005. The NASA center is within a 10-minute drive of Google's headquarters in Mountain View. Google anticipates needing the additional space for the thousands of workers it expects to hire as tries to mine more profits from the Internet's advertising market and expand into other areas of technology and media. In the last four years, Google has added more than 17,000 employees to boost its payroll to 19,156 workers. The growth has prompted the company to lease or buy many of the smaller offices circling its headquarters, a 1-million-square-foot campus that Google purchased for $319 million in 2006. The NASA deal sets Google's initial rent for 42.2 acres of land at $3.66 million per year. Google didn't estimate how much it would cost to build the new campus, which will begin construction in 2013 and will include some housing for employees. Google expects to start the final phase of the campus in 2022. After the 40-year lease expires, the agreement could be extended by as much as 50 more years. Google hopes the location of its new offices will make it easier to draw on the brain power of NASA's rocket scientists and give it another competitive advantage over its rivals. The close ties between Google and NASA caused a backlash last year when company co-founders Larry Page and Sergey Brin negotiated an unusual deal to take off, land and park their private jet at a government-managed airport near where the new offices will be built. Moffett Federal Airfield had been off-limits to most private planes, but Page and Brin got around that restriction by agreeing to pay NASA $1.3 million annually and making a commitment to fly the space agency's equipment on research missions.