Google, the most-popular Internet search engine, is expected to offer a new free e-mail service today, ratcheting up the competition with rivals Yahoo and Microsoft's MSN.

The e-mail, dubbed Gmail, will initially premiere as a test open to a few thousand invited users. If the technology performs well, the service will be made available to the public, probably within a few months.

Google's entry into e-mail, an increasingly important feature used to keep users loyal to a single Web site, comes as the company considers an initial public offering as soon as this year. The fact that the Mountain View company has added several features recently has fueled the speculation.

On Monday, Google premiered a personalized search function and system that allows users to automatically get e-mails when there's new information on the Web about a particular topic. In January, the company created a separate social networking Web site, called Orkut.

Wayne Rosing, Google's vice president of engineering, described Gmail as being in line with Google's mission of connecting users to information.

"We just belive that we are trying to add more value to our users," Rosing said. "Organizing all the world's information is our mission in life, and part of that information is each individual's information."

Gmail will be available only at www.gmail.com. Rosing said there are no plans to move the service to the main Google site.

Rosing said that part of Gmail's appeal is its large storage capacity, which allows users to avoid having to delete e-mails frequently. Individual mailboxes can hold up to 1 GB of data, or 166 times more storage than on Yahoo's free service and 500 times more than Microsoft's Hotmail.

Both Yahoo and Hotmail offer extra storage for a fee, but even those paid services are smaller than Google's Gmail.

Another advantage with Gmail, Rosing said, is its message organizing capabilities. For example, multiple messages in a single conversation would automatically be grouped together, allowing users to avoid searching their mailbox to reconstruct a conversation.

Gmail will be supported by text ads that appear in the margins of individual e-mails. Google software will automatically scan the messages for meaning, then try to offer relevant ads.

Sara Radicati, chief executive for the Radicati Group, a Palo Alto consulting firm that specializes in Internet messaging and collaboration, was skeptical of Google's e-mail efforts. Keeping the service on a separate Web site limits its visibility to potential users, she said.

Even if the service is moved to the Google home page, the company would face the significant hurdle of getting users to switch from their present e-mail providers, she said.

Yahoo and MSN's Hotmail already dominate the e-mail market, Radicati said. Yahoo has 30 percent of the world's active e-mail users, while MSN has 37 percent, according to her company's estimates.

"I think there's such a traction built up by Yahoo and Hotmail that it's going to be difficult to pry people away," Radicati said.