Microsoft Corp. has won a $617 million contract with the U.S. Defense Department to provide its latest software, including the Windows 8 operating system.

The three-year agreement announced Friday by the world’s largest software maker covers 1.5 million of the Pentagon’s computers.

The deal gives the Army, Air Force and Defense Information Systems Agency access to the latest versions of Windows 8 and programs such as Microsoft Office 2013 and SharePoint 2013, a file-sharing platform.

“The large majority of the United States Department of Defense just made the decision to go with Microsoft,” Tim Solms, general manager for Pentagon business at the Redmond, Washington-based company, said in a phone interview. “That’s very positive from a business perspective.”

The military received seven bids for the contract, according to a December news release. The competitors weren’t identified. The award went to a reseller of Microsoft products, Insight Public Sector, a division of Tempe, Arizona-based Insight Enterprises Inc.

Microsoft (Nasdaq: MSFT), long dominant in personal computers, has lost ground to smartphones and tablets championed by Apple Inc. and Google Inc.

U.S. retail sales of devices running Windows fell 21 percent from a year earlier in the four weeks after Microsoft released Windows 8 on Oct. 26, according to a Nov. 29 report by Port Washington, New York-based NPD Group Inc.

Windows Sales

The decrease has been fueled by a 24 percent drop in sales of notebook computers as customers opt for Apple’s iPad or tablets powered by Google’s Android software.

The Pentagon award is “a validation point for Windows 8 after the media has been fairly negative on it as an operating system,” Richard Williams, an analyst at Cross Research in Livingston, New Jersey, said in a phone interview.

“The fact that large organizations are adopting it adds credence to the idea that this software is an industry standard,” said Williams, who rates Microsoft shares a buy.

Brad Reback, an Atlanta-based analyst at Stifel Nicolaus & Co., said the agreement may buoy Microsoft’s business selling applications that compete with the Internet-based documents offered by Google.

Military Savings

The Pentagon deal also may allay corporate clients’ concerns about the security of some of the services that would be provided under the deal, Reback said.

While the contract shows the Defense Department’s support of Microsoft’s desktop operating system, it doesn’t necessarily mean all the users will convert to the latest version, said Reback, who rates Microsoft shares a buy.

“I don’t think this signals widespread adoption of Windows 8” within the Pentagon, he said in a phone interview. “Access is different than usage.”

The military expects to save “tens of millions” of dollars through lower software license costs under the agreement, according to a news release from the Defense Department.

The Pentagon represents about two-thirds of all prime, or direct, federal contract spending. The U.S. government awarded more than $530 billion in direct contracts in the fiscal year ended Sept. 30, 2011, according to data compiled by Bloomberg.