Here's one reason why the nation's largest cable company needs to reinvent itself: CBS is developing an online service for people to watch as an alternative to the early evening news.

"We call that the cable bypass," said Leslie Moonves, co-president of CBS's parent, Viacom Inc., at a recent investor conference.

Just 10 years ago, the cable industry had a virtual monopoly on the $56 billion market for piping TV into subscribers' homes. Now, a host of new technologies is threatening that business. In addition to battling the old enemy of satellite TV, cable operators are up against Internet companies, telephone operators and even television programmers, who, in various ways, are exploring how to sell TV to consumers. Their efforts suggest the possibility that soon, consumers will be able to watch whatever they want, when they want, without the help of the local cable company.

To protect its turf, cable giant Comcast Corp. has 400 software engineers building what amounts to a TV version of the Internet, stocked with movies, archived television programs and other interactive features, including a search function. Now, to push into the online-video business, among other reasons, the company is in talks with Google Inc. about teaming up to buy a stake in the Web operations of Time Warner Inc.'s America Online.

Internet-based technologies loom as an enormous threat to cable. Phone giants SBC Communications Inc. and Verizon Communications Inc. for example, are planning to use them to offer consumers a cornucopia of movies and TV shows that can be watched at any time.

Program owners are also getting in on the act. ESPN, the sports network owned by Walt Disney Co., is talking to consumer-electronics manufacturers about developing a set-top box that would show college-football games not available on cable or satellite. As was announced Wednesday, users of Apple Computer Inc.'s new video iPod will be able to watch five shows from Disney's ABC unit, including "Desperate Housewives" and "Lost," for $1.99 a pop. America Online is airing two original reality series, "The Biz" and "Project Freshman."

Brian Roberts, the chief executive officer of Comcast, is betting he can replicate enough of these newfangled services to prevent cable subscribers from defecting. One big advantage is Comcast's longstanding relationships with Disney, Viacom, Time Warner and other leading programmers. But he acknowledges that a major cultural shift is necessary. "We're genetically re-engineering ourselves," he says.

Already Comcast offers more on-demand programs and movies than most other cable operators, including 250 free movies, 500 music videos and 300 kids shows. In sports, it has NFL Replay, which shows highlights from football games played any given week. That's not counting the scores of shows available at any time from standard cable networks such as A&E, Oxygen and MTV. Comcast says it expects to have 10,000 programs available, up from 3,500 today, although the company won't give a timetable.

For now, many programmers say they're not planning to compete with the cable systems -- which are still the biggest pipeline into viewers' homes. Some are helping Comcast move into a high-tech future.

E.W. Scripps Co. provides material for the home page of Comcast's high-speed Internet service. Subscribers can click on scenes from shows about kitchen design, bedroom makeovers and growing cabbages that appear on Scripps's HGTV and Food Network. "We think first about how we can super-serve our partners who helped us develop these brands in the first place," says John Lansing, president of Scripps Networks.

But advocates of new TV-distribution technologies question how long programmers will stay loyal to the cable giants. Offering programs and movies on the Web, which is open to all, will be "too compelling from a content owner's perspective," compared with being enclosed within Comcast's proprietary system, argues Jeremy Allaire, founder of Brightcove Inc., a company that helps businesses put TV programs online.

Investors haven't shown much confidence in Comcast's strategy for fending off new competitors. At 4 p.m. on the Nasdaq Stock Market, Comcast's shares were down 40 cents at $27.92, close to the stock's 52-week low.

Last year, the company tried to buy Disney, largely for the trove of material it would have bought to Comcast's on-demand network. The deal collapsed because of negative reactions from Comcast investors and Disney's board.

More pointedly, investors worry that Comcast can't sustain growth in its core television business, which last year was responsible for $12.9 billion of $20.3 billion in revenue. Comcast has reported no cable-TV subscriber growth this year. Investors also worry about the cost of building these new technologies, especially in an industry notorious for spending billions on infrastructure.

In the 1990s, Comcast was happy to follow the lead of Time Warner, Cox Communications Inc. and other cable operators when it came to technology. Mr. Roberts acknowledges he was reluctant to make big bets for fear of making mistakes. The company, for example, was more than a year behind Time Warner in offering subscribers a digital video recorder. "Pioneers are the ones who get the arrows in their backs," Mr. Roberts liked to say.

Today, Cox and Time Warner are also working on ways to beef up their interactive TV offerings. Cox subscribers in northern Virginia will soon be able to check the local weather at any time, for example. But Comcast has taken a lead role in some areas. Compared with other operators, Comcast has more free on-demand content and is moving faster to switch subscribers from analog to digital signals, even though the transition won't be completed for years.

Comcast was vaulted into being a market leader largely by its 2002 acquisition of AT&T Broadband, which made it the country's largest cable operator with over 21 million subscribers in 35 states. For two years after the deal, Comcast's priority was integrating the companies. With that work mostly done, its focus has shifted to technology.

Dave Fellows, Comcast's chief technology officer, convinced Mr. Roberts to sign off on a plan that would transform Comcast's network into one run almost entirely on Internet technology. That would allow phone, broadband and TV services to travel over the same cable wires, making it easier to combine features, such as giving subscribers the ability to record shows from a Web site.

Another problem: Comcast's network is divided among 4,500 transmission centers, known as "head ends," which have limits on how much programming they can store. Partly to overcome this, Mr. Fellows is overseeing the development of a national fiber-optic network connecting 45 major cities. Comcast has leased 19,000 miles of cable from Level 3 Communications Inc. for $100 million. In the next few years, when programs are stored centrally, Comcast will have a virtually unlimited ability to store video data, matching phone companies' promised offerings.

To fill these new pipes, Comcast is building a library of shows and movies through deals with established programmers such as Discovery Communications Inc. and Viacom's MTV. It's also trying to lure viewers by pitching services only available from Comcast. Its Irving, Texas, system, for example, will show 25 high-school football games this season. The Philadelphia system is testing an on-demand real-estate service that enables viewers to participate in virtual tours.

Comcast has also rolled out an on-demand dating service featuring singles in eight cities. It dispatches production crews to bars, college campuses and even street corners where they convince singles to tape descriptions of their romantic aspirations. The segments are searchable by gender and age. One event the company sponsored at M&T Bank Stadium in Baltimore earlier this year attracted thousands and kept seven production crews busy.

Comcast is also pouring money into new technology to allow subscribers to search through its television-program library. Just 18 months ago, Comcast's interactive TV guide consisted of little more than a grid showing channels and times on a tan background. About one-third of the screen was an ad. Unlike other guides, viewers couldn't watch shows while browsing through the grid.

Comcast has added that feature, dropped the ad, expanded the grid and organized on-demand offerings under headings such as movies, news, kids and teens and lifestyle.

Last year, Comcast paid $250 million for a majority stake in the on-screen guide business of Gemstar-TV Guide International Inc. Gemstar, which publishes TV Guide magazine, is 41 percent-owned by News Corp. Renamed GuideWorks, the on-screen unit now employs 160 of Comcast's new software engineers. Its $26 million research budget is more than double what Gemstar-TV Guide was spending.

A soon-to-be released version of Comcast's interactive guide borrows from the experience of navigating the Internet. When the TV is turned on, most viewers will see a home page with choices, including "On Demand" or "Main Menu." A group of four screens will show what's happening on different channels.

Comcast executives acknowledge that their search technology is still limited. You can't pick the channels airing on the four screens -- technicians in Comcast's Denver network center control what's appearing. Typing names of shows using a remote is awkward.

In future versions, GuideWorks is looking at ways to recommend shows based on a favorites list. Comcast subscribers may also be able to do keyword searches for TV shows on their computers and have the results communicated to their TVs. Comcast won't say when this could be available.

Earlier this year, Comcast cut a deal with Motorola Inc. which gives Comcast more control over the development of its set-top box. The company has also acquired two software companies and cut a deal with TiVo Inc. to customize its digital video recorder service for Comcast subscribers.