SAN FRANCISCO — Online search engine leader Google Inc. is wedding its instant messaging and e-mail services in the same Web browser, hoping the convenience will lure users from the larger communications networks operated by its chief rivals.

The new chat feature to be unveiled today will provide users of Google's Gmail service with a list of contacts drawn from past e-mail exchanges and then signal who is available for online conversations.

Automatic status reports about the online availability of friends, family and co-workers have been a hallmark of instant messaging services for years.

Google hopes to make it even simpler to connect with an online contact by allowing users to initiate an electronic conversation within the same Web browser showing an e-mail mailbox, bypassing the need to switch to a separate instant messaging application.

The new chat feature will begin to show up in some Gmail accounts Tuesday and should reach all users within the next few weeks, said Salar Kamangar, a Google product manager.

"We didn't think it made sense for there to be this artificial separation that currently exists between e-mailing and chatting," he said. "People don't want to have to have two separate contact lists for e-mail and instant messaging."

The new chat feature only will work if both users have Gmail accounts or belong to a service compatible with Google's instant messaging service. Besides Google's own services, the network includes EarthLink, Jabber.org, Sipphone's Gizmo Project, Chikka in the Philippines, Singapore's MediaRing, Italy's Tiscali and China's Netease.

By further blurring the lines between instant messaging and e-mail, Google is hoping to gain ground on the current market leaders — Yahoo Inc., Microsoft Corp. and Time Warner Inc.'s America Online.

Google introduced its e-mail service in April 2004 and unveiled its instant messaging service last August, long after the market leaders had amassed loyal audiences.

The communications services are valuable because they help foster user loyalty and give people another reason to return to a Web site. Google expanded into the field so it would have more chances to display the online ads that account for most of its profits, which totaled $1.5 billion on sales of $6.1 billion last year.

Although none of the free e-mails disclose how many account holders they have, Yahoo's is the most frequently used, followed by AOL and Microsoft's MSN and Hotmail, according to Nielsen/NetRatings Inc. Yahoo's e-mail service hosted nearly 51 million unique visitors in December followed by AOL at 34 million visitors and Microsoft's services at 31 million.

AOL leads the pack in instant messaging with nearly 53 million users in December, trailed by MSN at 27 million and Yahoo at 22 million, Nielsen/NetRatings said. Google's instant messaging service ranked as the sixth most used with 866,000 users.

Google is hoping the feature will encourage more Gmail users to invite their friends, family and co-workers to open accounts, Kamangar said. The Gmail service has been available on an invitation-only basis since its inception, another factor that has limited its appeal.

Despite its relatively small audience, Gmail has helped to reshape the e-mail market by offering its users far more free storage than its rivals. The largest services subsequently have increased their storage capacity to remain competitive with Gmail's current offer of nearly 2.7 gigabytes per account.