Google Apps for Government exceeds US federal information security requirements, according to IT services firm Unisys.
The contractor led a project to move the first of the US government's 15 agencies to Google's cloud-based services, according to US reports.
Officials at Unisys say the Google deployment provides two-factor authentication using technology from SecureAuth, a rival of the widely-used RSA SecurID system.
Now the General Services Administration's (GSA's) 17,000 employees can access their e-mail, share documents and chat without having to log on to the agency's network.
In announcing the $6.7m project last December, GSA officials said the shift would cut costs in half over a five-year contract period, partly by reducing equipment and staffing needs as Google will manage all the hardware and software requirements.
Outsourcing IT to the cloud is part of a federal effort to save $3bn over five years by shutting down about 40% of the government's 2,000-plus computer centres.
Earlier this month, the White House announced it will close 178 data centres in 2012, after phasing out 195 by the end of 2011.
Google, Microsoft, IBM and Amazon are competing for a share of the federal cloud services market.
The Federal Cloud Computing Strategy report has identified $20bn in spending that could be moved to the cloud.
In April, 15 agencies identified 100 e-mail systems that will be moved to the cloud. Unisys has set a target date of December for transferring 25,000 employees at the Commerce Department's National Oceanic and Atmospheric Administration from various e-mail systems to Google's service.
But IT experts consider e-mail the "easy sell" of the move to cloud-based servies. They say agencies will take longer to accept cloud-based storage, computing power, website hosting and other infrastructure.