CBS said on Thursday it will stream its prime-time news program with Katie Couric live on the Internet simultaneously with the newscast, a first for a major TV network that highlights U.S. broadcasters' rapid expansion on the Web.

The Web casts will begin when Couric first sits in the CBS Evening News anchor chair on September 5 in a high-profile arrival after leaving her co-host job on NBC's Today morning show.

Couric takes the post that previously was held by Dan Rather and before that by Walter Cronkite, in a move aimed at boosting CBS from its No. 3 position in network news viewership.

In the week ended August 11, for instance, rival NBC averaged about 8.1 million viewers a night compared with ABC's 7.5 million and CBS's 6.9 million, according to Nielsen Media Research.

CBS's move to simulcast the Evening News and provide other Web content, such as a Couric & Company blog, also marks a new way for it to win wider audiences. Spokesmen for CBS's rivals were quick to point out that they offer Web content, too, although not live simulcasts of nightly news.

In a statement, CBS called its strategy a groundbreaking development.

It's another giant step toward providing CBS News content to people wherever they are - in their homes, in their offices, in their cars, on their computers or on their cell phones, said Sean McManus, president of CBS News and Sports.

In the past year, as high-speed broadband Web connections to homes and offices have reached mass market levels, the demand for video online has greatly increased and networks are now offering some shows for downloading on-demand.

NBC offers NBC Nightly News with anchor Brian Williams on-demand after the live newscast, and the network puts out a Web blog on the day's news-gathering called The Daily Nightly.

ABC puts up a 15-minute original Web cast called World News every afternoon, and it also offers a blog.

CBS will match and try to exceed its rivals' efforts. CBS said the Evening News will be available on-demand, and it unveiled another new Web show, Eye to Eye, hosted by Couric and featuring extended interviews which will be available on-demand.

Other Internet content will be CBS News First Look with Katie Couric, a live Web cast from the CBS news floor early in the morning, and Katie Couric's Notebook, a one-minute glimpse of a top story or an important issue.

CBS is owned by CBS Corp., NBC is a unit of the NBC Universal media division of General Electric Co., and ABC is part of the Walt Disney Co..