Yet both have something working in their favor: They rank No. 1 and No. 3 among broadcast networks online, respectively. PBS is No. 2.

They're seeing more visitors primarily because they've done more to attract them, posting more content and making that content easier to get to.

Exactly what that means for either NBC or ABC is unclear, including the impact it’s having on TV ratings. A new IBM study reports that half of people who watch shows online say they're watching less TV as a result.

Still, media buyers think the networks have done a great job of building out their brands to the internet, and presumably that will benefit them as more viewers and ad dollars shift to the web.

NBC was No. 1 online the week of Nov. 8, accounting for 23 percent of the online broadcast network audience, according to Hitwise.

“NBC has been very proactive in promoting all the different platforms, all the screens,” says Brad Adgate, senior vice president and corporate research director at Horizon Media. “They’re looking to the future.”

PBS was No. 2 at 22 percent. ABC had 21 percent of the audience. CBS had 16 percent and Fox had 10. Muddying these numbers, hulu.com--a joint venture between Fox and NBC--ranked No. 8 among video sites.

In a separate study, Nielsen Online found NBC.com had 5.6 million visitors in September. ABC.com was No. 2 with 5.2 million. CBS.com had 3.3 million and Fox.com had 1.4 million visitors.

But in reality all are probably attracting larger online audience to their shows than those numbers suggest, since their shows are available through other online outlets, notably Hulu.

All the networks post full episodes of at least some of their shows, along with online-only content, and they've stepped up their marketing efforts, online and off, to build traffic.

NBC puts virtually all its programming online, including some episodes that air online before they’re on TV. “30 Rock” premiered online a week before it aired on TV, and yet it still scored its best-ever season premiere rating.

NBC also built up an online following with thousands of hours of Summer Olympics programming and, in recent months, election-related content.

“I think the ‘Saturday Night Live’ clips were huge for them,” says Chris Allen, vice president and video innovation director at Starcom USA. “That drove a ton of traffic.”

And NBC puts original content on its site, including for shows like “Heroes,” “The Office” and game show “Deal or No Deal,” the No. 1 online show the week of Nov. 8.

ABC and Fox do a good job luring in viewers with additional content and information, notably for their reality shows. ABC’s “Dancing with the Stars” was No. 2 the week of Nov. 8.

Media buyers fully expect Fox to zoom to No. 1 online when “American Idol” returns in January.

“We have about 20 or so shows with full-length screening and we syndicate our content to Hulu,” says Bill Bradford, senior vice president of content strategy at Fox. “We also have external marketing for our content on many places around the internet.”

PBS also puts much of its content online, often full episodes the day after a show airs on TV. During the recent elections it had a slew of content about candidates on its sites.

PBS also actively promotes its content online, in part through a complex search engine optimization strategy to get itself highly ranked on search engines like Google.

Moreover, it posts some of its content on social networking sites such as Facebook, says Kevin Dando, director of education and online communications at PBS.

“Our kids’ web sites and our general-audience web sites are way up across the board,” he says. “One thing we think is affecting that is social media sites. We’re getting a lot of traffic from sites like StumbleUpon, YouTube and Facebook. In some cases, we’re seeing triple-digit increases over last year.”