On July 7, the day of the terrorist bombings in London, MSNBC.com logged an extraordinary 10.3 million unique visitors who viewed more than 51 million pages and clicked their way through 4.4 million on-demand video streams. Foxnews.com that day broke the million-stream mark, logging more than 1.1 million streams. And AOL News reported more than 300,000 live video news streams by 2 p.m. (ET) that day and more than 1.75 million page views related to the bombing.

Web site traffic and video streaming demand records are being set with each major news event, especially those that occur during business hours. Traffic on average news days spikes dramatically during lunch hours. “On the Web, daytime is prime time,” said CBS Digital Media President Larry Kramer.

That is one of the reasons CBS News, the TV news organization perhaps most defined by its past, is going online in a big broadband way in an attempt to redefine, revitalize and perhaps even reinvent itself as a 24-hour high-speed news organization.

“What took so long?” was the reaction from some competitors who were quick to note that CBS News, which is the only one of the Big 4 broadcasters without a 24-hour cable news outlet, was also last to identify broadband video news on-demand as the next big wave in TV news.

“It’s a logical place to be in today’s news climate,” said Catherine Captain, VP of marketing for MSNBC.com, adding that CBS’s new strategy only “further validates the medium.”

It’s a medium that has been growing by the proverbial leaps and bounds. An estimated 45 million people are said to have access to high-speed Internet connections at work. In addition, broadband access at home is expected to rival cable penetration by the end of the decade. According to recent projections by TNS Media Intelligence, advertising revenue on the Internet is expected to grow this year by 7.6 percent after two years of double-digit growth.

The move to expand news on broadband isn’t new. ABC News Now, a 24/7 digital news service whose forebears include the first Webcast, featuring Sam Donaldson, which debuted in 1999 to an audience of less than 1,000 people. Today it is available to more than 30 million online and mobile subscribers.

“Long term, we look at a hybrid of subscription and ad-supported as the revenue model for the future,” said Bernard Gershon, senior VP and general manager of ABC.com’s Digital Media Group.

NBC News President Neal Shapiro said it will “take awhile” for the full online revenue possibilities to be realized, but he added, “MSNBC.com is doing quite well. The Web is clearly a growing part of advertising.”

The CBS broadband content, which will expand and evolve over the next few months, will be ad-supported and remain free to users, as are MSNBC.com, Foxnews.com and CNN.com, at least for now. CNN is expected to introduce new broadband options later this year that consumers will pay to watch.

The CBS broadband content will include Web logs by beat reporters, a blog titled “Public Eye” designed to facilitate a dialogue with the public about CBS News, and a “video jukebox” that will enable users to build their own personal newscast.

Mr. Shapiro said that blogs on MSNBC.com have proved popular with the public and the bloggers, who like the chance to write something shorter and more personal than the stories they do for TV and who include “NBC Nightly News” anchor Brian Williams. The NBC News president also said that viewers who respond to the NBC and MSNBC bloggers “are very touched when they get responses.”

CBS News President Andrew Heyward acknowledged that the “philosophical shift” toward the Internet, where breaking news will be emphasized, will have an impact on any plans to revamp “CBS Evening News,” so that the flagship newscast feels neither outdated nor so second-dayish that it disappoints Web users or alienates core viewers.

Bob Schieffer, the interim “Evening News” anchor, will also anchor an online edition of “Evening News,” since CBS is bound by agreements with affiliates not to repurpose the flagship broadcast.

Betsy Morgan, who has managed CBSNews.com since 2001 as the CBS News VP of business development, will transfer to CBS Digital Media as senior VP and general manager of the new Web site. She is expected to make hires to beef up the Web operations.

Mr. Kramer said a variety of advertising options will be available on CBSNews.com, from shrinking banners, pre-roll ads attached to video and interactive ads to positions that can be sold across other CBS-family Web sites, which attract some 20 million unique visitors per month. “There’s no question that advertising drives us,” Mr. Kramer said.

Aside from the increasing audience for online, on-demand news and information, what piques advertisers’ interest is the demographics of Internet use. “About half of our audience is [in households making] $75,000 or over,” said Bert Solivan, VP of news and information and general manager of Foxnews.com.

Internet news audiences also tend to be significantly younger than TV news viewers. The average age of CNN.com users is 42.3, the lowest of the major TV news organizations’ Web sites, according to data from @Plan, a third-party syndicated research company. The average age for MSNBC.com is 44.1, the average for Foxnews.com is 44.7 and the average age for ABCNews.com is 45.2.

The average age for CBSNews.com users tops this list at 46.4. The average age of “CBS Evening News” viewers is 59.9, so a beefed-up Web site might not only drive more viewers to the news organization but also might drive younger viewers to the third-ranked signature morning and evening newscasts.

Some competitors said the plans for CBSNews.com do not dramatically change the Internet news landscape, but most agreed that the more players the better for all the players. “Ubiquity is a good thing,” said Fox’s Mr. Solivan. “The more people get used to it, the more people demand it.”