Google Inc's highly anticipated real-time communications service is not ready for prime time, but the company said on Tuesday it was on track to begin the biggest field test yet of the potentially groundbreaking Google Wave.

The Internet search leader intends to launch a limited preview of the service, already tested by developers and considered one of the company's most promising innovations as it seeks to widen its footprint among corporate clients.

Experts say the project has the potential to advance Google's plans to provide software to corporations, as well as giving Google a bigger role in a social networking space now dominated by companies like Facebook and Twitter.

Wave, first announced in May, aims to combine instant messaging, email, document handling and social networking features in one package.

In a pair of posts on the official Google blog on Tuesday, it also said it was exploring plans for a monetizable wave extension store that would allow developers to sell software that enhances the service's capabilities.

The comments come a day before Google is due to send invitations to access Wave to more than 100,000 developers, individual testers and select corporate users of Google Apps -- a suite of office-oriented applications from email to word processing -- in the biggest field test of the new service to date.

Wave was developed by a small team in Australia, led by brothers Jens and Lars Rasmussen.

Some of you have asked what we mean by preview. This just means that Google Wave isn't quite ready for prime time. Not yet, anyway, wrote Lars Rasmussen in Tuesday's post. He noted that Wave still experiences occasional downtime, crashes and sluggishness.

He said that Google will allow some of the new Wave preview users to nominate friends, family and colleagues to use Wave, and it will soon invite many more people to try the service if all goes well during the preview.

In a separate blog post on Tuesday, Wave Product Manager Stephanie Hannon cited efforts by companies like SAP and Salesforce.com Inc to develop software prototypes that extend the capabilities of Wave, as well as products that add video conferencing, trip planning tools and games like Sudoku puzzles to Wave.

To help foster a strong developer ecosystem, we're exploring plans for a monetizable wave extension store, wrote Hannon.

Google has not given a public timeframe for Wave's general availability, though the home page of the official Wave Web site says the service is coming later this year.

(Reporting by Alexei Oreskovic; Editing by Phil Berlowitz)