Starting today, “Today” viewers can get up later or leave the house earlier without fear of missing the first hour of the NBC morning show.

NBC is debuting an Internet broadcast of “Today,” which leads the morning ratings, that features more material than do Web offerings from rivals “Good Morning America” and “The Early Show.”

The Web project, led by NBC News VP of Digital Media Mark Lukasiewicz, will be supported by advertisements that viewers won’t be able to skip.

NBC is introducing the “Today” webcast as Jeff Zucker, CEO of NBC Universal Television Group, pushes television producers to pitch programs that include material for the Web, cellphones and other technologies. Networks are scrambling to generate advertising revenue and retain viewers who increasingly demand to watch programs when and where it’s convenient.

The “Today” webcast builds on other Internet offerings from NBC’s news division, which in 2005 began streaming “NBC Nightly News” and “Meet the Press.”

“We have gained a huge good will component from our users” with those Web programs, Mr. Lukasiewicz said.

With Internet broadcasting still in its infancy, NBC is trying various approaches to generate revenue. The Web version of “Nightly News” has two sponsorship spots and “Meet the Press” has one. Each hour of the “Today” webcast will accommodate four 15-second spots.

“It’s yet another indicator that the ad-supported model for broadband video is becoming attractive to major program providers, and we expect that’s going to continue in the future,” said Will Richmond, founder and president of Broadband Directions, a market intelligence and consulting firm.

Three-quarters of the available ad time in the “Today” webcast has been sold for the first month, mostly to automotive and pharmaceutical companies, said John Kelly, senior VP of NBC News network sales.

Mr. Kelly declined to provide specifics about the pricing for advertising on the “Today” webcast. “We always look for the upside, so we don’t want to undersell it,” he said.

Translating “Today” onto the Web requires changes to the show. NBC’s MSNBC partner Microsoft Corp. will replace ads seen on the network with Internet spots. The webcast won’t offer local news or weather windows because that kind of customization isn’t yet feasible for a national show, Mr. Lukasiewicz said.

By putting only the first hour of “Today” on the Web, NBC News reduces some of the complications presented by the liberal use of music in segments that tend to appear later in the show, as the subject matter gets lighter.

“We’re not ruling out the rest of the show as a netcast,” Mr. Lukasiewicz said. “But we thought, ‘Let’s start with the first hour. It’s a good length. It works for us.’ Any music and rights issues we might have are certainly smaller in that hour, and we can deal with them. And then we’ll go forward.”

Keeping the webcast to an hour also lets NBC get the show online by lunchtime, when Web traffic rises, the NBC executive said.

“We have a very heavy usership during the middle of the day,” Mr. Lukasiewicz said.

So far, Web users are only a fraction of a network’s audience.

“Here’s what we have learned,” Mr. Lukasiewicz said, referring to his division’s Web offerings. “So far, the usership, the viewership is not massive.”

An average of 250,000 people per month view “Nightly News” on the Web, he said.

The “Today” webcast supplements a show that has led in the morning ratings for more than 10 years. The program averaged 5.9 million viewers the week of April 17, compared with 5 million for “Good Morning America” and 2.8 million for “The Early Show,” according to Nielsen Media Research.

A spokeswoman for “Good Morning America,” which also makes a selection of segments available on ABCNews.com and to subscribers of the ABC News Now broadband service, said the network has no plans to offer a more complete streaming version of the ABC morning show on the Web.

A CBS News spokeswoman said there are no immediate plans for a Web version of “The Early Show.”

The decision to package “Today” for the Web was driven more by the NBC News strategy of making programming as accessible as possible on new media than by the prospect of immediate riches, Mr. Lukasiewicz said.