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

Profit at the world's largest software company slid to US$6.4 billion (S$7.9 billion), or 76 US cents per share, in the fiscal second quarter, from US$6.6 billion, or 78 US cents per share, in the year-ago quarter.

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

Overall sales rose 3 per cent to US$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 per cent to US$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 per cent to US$5.9 billion.

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

Microsoft shares fell slightly in after-hours trading.