On the first night of what would become the 24,000-acre Topanga fire, KABC-TV executive Bill Burton decided it was time for Channel 7 to expand its digital offerings.

Just before Eyewitness News was about to make way for the network’s “ABC World News Tonight,” anchors alerted viewers that if they wanted to continue watching coverage of the growing firestorm, they could tune their digital TVs to ABC7Plus, its digital broadcast channel.

It was a bit tricky for the uninitiated if they had an outside antenna, they tuned their digital TV to D2. If they had digital cable, the station depended on the cable provider. But those who succeeded were able to watch Eyewitness News crews continue live coverage for another half hour.

“It’s something we’d been considering trying for a long time and this seemed like an appropriate opportunity,” said Burton, vice president of programming, advertising and promotions. “That night the story had grown to the point where there was interest in covering it a while longer, but it wasn’t big enough that it warranted pre-empting the network news like we did the next night.”

In addition to the high-definition version of Channel 7, KABC programs two additional over-the-air digital channels one providing local weather radar and the other offering a mix of rebroadcast local and network news shows, some syndicated programs and a few infomercials. But on a high-interest local story like the first major wildfire of the season, ABC7Plus, also known as Channel 7.2, can provide the station with the flexibility of a 24-hour news network.

Though ABC has been among the most aggressive in promoting its digital and broadband offerings, its L.A. station appears to be one of the first to use part of its share of the digital spectrum as an extension of the primary channel.

“We certainly think the technology and time is right to be offering our programming on a whole variety of platforms,” said Bernard Gershon, senior vice president and general manager of the ABC News Digital Media Group.

Gershon echoes a message promoted for months by Robert Iger, chief executive of ABC parent Walt Disney Co., about being a “platform-agnostic” provider of content that can be accessed by cell phone or video game unit, in addition to TV, radio and computers.

Cable access to Channel 7.2 has only recently been added by all the region’s five major cable providers. Though the station’s Web site provides tips on how to watch Channel 7 on a cell phone, and even how to send news photos to the station via camera phone, there’s little information about the digital broadcast channels.

“These are uncharted waters for us,” said Burton, adding that the station plans to further diversify programming on Channel 7.2, and soon will upgrade its third digital broadcast channel, D3 or Channel 7.3, to 24-hour local weather programming from AccuWeather Inc.

While critics say that broadcasters have been slow in developing programming for the digital spectrum they got for free from the federal government in the late 1990s, local media experts note that it’s only recently that a critical mass of viewers with HD-ready TVs and other high-tech media toys have emerged to justify the investment.

“The Federal Communications Commission gave them a chicken and the networks to date have laid an egg,” said Howard Suber, professor emeritus and founding chair of the UCLA Film and Television Producers Program (and owner of four HD TVs at home). “With a few exceptions, the networks and affiliates haven’t been jumping into HD as fast as the FCC thought they would, and that’s because of the money involved.”

Jeff Cole, director of the USC Annenberg School Center for the Digital Future, notes that the networks went through the same struggle during the conversion to color television. NBC was a pioneer in color programming, in large part because its parent, RCA, stood to make a lot of money selling color TVs.

CBS was the first to produce major shows in high definition format because its executives realized that the syndication rights for hit shows like “CSI” would be less valuable in standard format when HD sets become common in several years.

Cole applauded KABC’s experiment with extended live programming on Channel 7.2. “There are a lot of interesting uses for this digital spectrum and this certainly is one of them,” he said.