One of the biggest social media sites on the Internet will soon allow you to attach files created in Microsoft Office products.

Microsoft today announced that its Office Web Apps will be integrated with the new Facebook messaging that was unveiled yesterday.

Users will be able to view the files but not alter them if you don’t have a copy of Office installed on your computer. If you’ve got a copy, you can download and make any changes you want to the file or files.

Facebook’s messaging service, which blends e-mail, instant messages and text messages into a single inbox, will support attachments of Microsoft Word, Excel and PowerPoint documents, according to Takeshi Numoto, an executive in the Office group.

Users who lack a copy of Office installed on their computers will be able to view Facebook-delivered Word, Excel and PowerPoint attachments using Office Web Apps, said Numoto.

Office Web Apps is Microsoft’s stripped-down, online-only version of its desktop suite. The online applications — Word, Excel, PowerPoint and OneNote — launched in June.

A single-click on the Facebook-delivered attachment — by choosing “View on Office.com” — displays the document in the user’s browser. Alternately, people can click “Download” to download the file, which can then be opened with Office, assuming the suite is on the machine.

Office Web Apps supports Internet Explorer 7 and later, Firefox 3.5 and later, Chrome and Safari 4 and later.

Microsoft is retaining the mash-up Docs.com, which lets Facebook users share Office documents. Microsoft’s Fuse Labs group launched that service last April.

“[Docs.com] will continue in parallel as we continue to test how ‘the social’ and productivity come together for users,” a Microsoft spokeswoman said today.