Microsoft confirmed that it has begun “Release Candidate” testing on Office 2010, triggering suspicions among some observers that the productivity suite may ship earlier than expected.

The copies being distributed, which are in the last testing phase before the product’s release — thus the name “Release Candidate” or RC — are going out to members of Microsoft’s (NASDAQ: MSFT) Office 2010 technology adoption program, or TAP.

TAP is a long-running initiative that aims to involve important Microsoft customers in testing and providing feedback on product development. By definition, TAP participation is limited.

“Microsoft made a release candidate available to members in the technology adoption program,” a Microsoft spokesperson told InternetNews.com in an e-mailed statement.

“This is one of Microsoft’s planned milestones in the engineering process,” the spokesperson said. “However, they do not have plans to make this new code set available broadly.”

The question of whether there will be a later, broader RC test remains unanswered — the spokesperson declined to comment on that possibility.

Office 2010 has been in beta testing since Microsoft’s Professional Developers Conference in Los Angeles in November, and the company said Wednesday that there have been more than 2.5 million downloads of the beta. Microsoft also made earlier releases of Office 2010 available as community technology previews (CTP) for almost a year prior to the beta test.

In early December, company officials said Office 2010 will ship in June, a date that has remained stable for some time.

Prior to officially designating June as the ship date, Microsoft had been promising that the latest version of its premier applications suite would ship by the end of the current fiscal year, which, conveniently enough, ends on the last day of June.

However, some technology enthusiasts and pundits are predicting Office 2010 may ship earlier, after Microsoft CEO Steve Ballmer told an audience in Tennessee last week that the suite would be out “in just a couple of months.

That raised eyebrows and led several veteran Microsoft watchers to suggest Office 2010 could ship prior to June, perhaps much sooner.

“You know those under-promise/over-deliver-focused Office guys always like to beat their own deadlines. I’m expecting they’ll do it again this time around … and by more than a few months,” industry blogger Mary Jo Foley said in a post on Tuesday.

Early last month, Microsoft announced packaging and pricing for Office 2010. Pricing for the various stock keeping units, or SKUs, remained similar to Office 2007. However, the company also said it is eliminating the Office Ultimate SKU and adding a new one called Academic Professional.

Among the differences between Office 2010 and its predecessor, Office 2007, is the addition of Web versions of the main productivity applications — Word, Excel, PowerPoint and OneNote — which will run in Internet Explorer, Firefox and Safari browsers.