SEATTLE (Reuters) - Microsoft Corp said its quarterly profit fell as Office software sales slowed ahead of a new launch, offseting a solid start for its new Windows 8 operating system.

Profit at the world's largest software company slid to $6.4 billion, or 76 cents per share, in the fiscal second quarter, from $6.6 billion, or 78 cents per share, in the year-ago quarter.

Wall Street had expected 75 cents per share, on average, according to Thomson Reuters I/B/E/S.

Overall sales rose 3 percent to $21.5 billion, Microsoft said on Thursday, in line with analysts' estimates.

With the loss of some deferred revenue to account for discounted upgrades to new software, Office revenue fell about 10 percent to $5.7 billion, which is not unusual ahead of a new launch, expected next week.

Windows sales, which included some deferred revenue from the launch of Windows 8 last October, jumped 24 percent to $5.9 billion.

Microsoft said it has sold more than 60 million Windows 8 licenses since launch, a solid but unspectacular start for its latest operating system.

Microsoft shares fell slightly in after-hours trading.

(Reporting by Bill Rigby; Editing by Richard Chang)