Fretting over eroding network television viewership and weak advertising, big media companies are now scrambling to distribute ad-supported content online.

ABC today announced a deal to distribute television shows through AOL, following NBC, CBS and Fox, which also have such deals.

Separately, NBC Universal said it will allow users to download its television shows and watch them for free for one week after they are broadcast.

The NBC Direct program, to begin testing in October and launch in November, will have shows would have commercials embedded within them and would not be transferable to other computers. Next year, NBC hopes to offer downloadable shows that users could buy and then move to other computers or devices.

The venture is part of NBC’s attempt to find a way to generate new revenues from its television content. NBC recently pulled out of a deal it had with Apple to distribute content via iTunes, because Apple would not change its pricing structure.

The NBC Direct announcement, however, had some observers scratching their heads because NBC already has a deal with News Corp. to aggregate and distribute content on their jointly-owned Hulu website. With Hulu distributing content to AOL, MSN, MySpace, and Yahoo, some wondered why users would need to use NBC Direct. And Hulu has been delayed, while competitors like YouTube, Amazon Unbox, and MySpace TV are building their own programming and distribution.

Walt Disney’s ABC for its part is also feeling out its own strategy. Like other media companies, ABC is no longer content to simply present its content on its own website. It is instead seeking to distribute its material as widely as possible through large Internet partners. 

To appease local ABC affiliates, ABC will use so called contextual targeting information from web surfers to serve locally-based advertisements with the AOL-distributed content.

Many analysts still wonder whether big media companies can generate revenue through online distribution. Web surfers are traditionally thought to be more interested in “video snacking”—watching short video clips such as those found on YouTube—than watching full length television shows.