Google Inc. is taking the wraps off an Internet encyclopedia designed to give people a chance to show off - and profit from - their expertise on any topic.

The service, dubbed “knol” in reference to a unit of knowledge, had been limited to an invitation-only audience of contributors and readers for the past seven months.

Now anyone with a Google login will be able to submit an article and, if they choose, have ads displayed through the Internet search leader’s marketing system. The contributing author and Google will share any revenue generated from the ads, which are supposed to be related to the topic covered in the knol.

The advertising option could encourage people to write more entries about commercial subjects than the more academic topics covered in traditional encyclopedias.

Since Google disclosed its intention to build knol, it has been widely viewed as the company’s answer to Wikipedia, which has emerged as one of the Web’s leading reference tools by drawing upon the collective wisdom of unpaid, anonymous contributors.

But Google views knol more as a supplement to Wikipedia than a competitor, said Cedric Dupont, a Google product manager. Google reasons that Wikipedia’s contributors will be able to use some of the expertise shared on knol to improve Wikipedia’s existing entries.

With a seven-year head start on knol, Wikipedia already has nearly 2.5 million English-language articles and millions more in dozens of other languages.

Knol is starting out with several hundred entries. The initial topics covered include an overview of constipation by a University of San Francisco associate professor of gastroenterology and backpacking advice from one of Google’s own software engineers.