On a day that Google augmented Gmail with a social networking feature, Facebook and AOL announced a partnership that will allow millions of their users to add friends and chat across the Web environments.

Tuesday’s dueling announcements underscore the growing rivalry between Google, the Internet’s leading company, and Facebook, which recently passed AOL to rank third in Web traffic.

The alliance integrates Facebook Chat into AIM, AOL’s instant messaging platform, and its new Lifestream feature. Lifestream already provides many of the same updates and social features that Google is now introducing with Google Buzz, said Brad Garlinghouse, a former Yahoo executive who now leads AOL operations in Silicon Valley.

AIM is the first major instant messaging service to integrate with Facebook’s new interface. “In today’s online environment, you can’t be competitive without being open and allowing partners, developers and consumers to leverage your technology,” said Ethan Beard, Facebook’s director of platform marketing.

About 70 percent of AOL users also use Facebook. The integration with Facebook, Garlinghouse said, “is a sign of where AOL is heading” as it tries to restore its reputation as an Internet innovator.

Contact Scott Duke Harris at 408-920-2704.