SEATTLE — Microsoft, the world’s biggest software maker, will introduce a new, free Web-based email portal under its Outlook brand and phase out Hotmail over time as it seeks to draw users from Google’s Gmail.

A preview of the new service was set to be online by today, and Hotmail probably will be phased out in the next year, said Brian Hall, a general manager in Microsoft’s Windows group.

By going with Outlook, Microsoft is trying to capitalize on the brand behind the most-used corporate email service, sold as part of its Office suite.

While Hotmail is the world’s most popular Web-based email provider, it has lost ground in the United States to Google and Yahoo as well as other, newer methods of communication, such as social media.

“Email is one of the only areas in technology that’s gone eight years without a significant change, the last big move was the release of Gmail, and for us it’s maybe been even longer than that since our last big change,” Hall said. “None of the social networks existed then, and the types of email we get have changed.”

Hotmail was the only one of the top three Web-mail services to lose unique visitors globally in the year through June 2012, falling 4 percent, according to ComScore. Yahoo Mail gained 2 percent and Gmail increased 17 percent.

Hotmail had 324.2 million unique visitors in June, compared with 290.3 million for Yahoo Mail and 277.6 million for Gmail, according to ComScore.

Users who want to upgrade can choose between keeping their existing hotmail.com email address or switching to outlook.com. Switchers will still receive mail sent to the old address, Microsoft said.

While Hotmail generates revenue through ads, the main value lies in how often people use email, Hall said. Google is using Gmail to lure customers to its online word processing and spreadsheet applications and away from Microsoft’s Office.

The Outlook Web-mail service can tell whether an email is from a personal contact, in which case it shows content from Facebook and Twitter from the sender.

Users will be able to see if a sender is online and enter into a Windows Messenger or Facebook chat session with them.