he Federal Communications Commission unanimously approved a method yesterday for broadcasting digital radio within current analog channels.

And in a move likely to speed adoption of the technology, the agency endorsed a patented approach for delivering such services developed by iBiquity Digital, a privately held company whose investors include the nation's 15 largest radio broadcasting companies.

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The technology enables broadcasters to begin sending digital signals while also continuing to provide standard AM and FM analog service to listeners who do not own receivers able to pick up the digital programming. "Radio can now formally begin its long-awaited digital transformation," said Robert J. Struble, president and chief executive of iBiquity, which is based in Columbia, Md., and Warren, N.J. "It's the most significant advance since the introduction of FM radio."

The first digital radio broadcasts are expected before the end of the year. But the equipment to receive the signals will not be available to listeners before next spring. A digital car radio is projected to cost $100 or so more than a comparable analog receiver.

Digital radio broadcasting promises clearer sound than conventional analog transmissions, and the ability to transmit streams of data along with audio programming. But it has been delayed by regulatory and technical concerns. Today's F.C.C. ruling, coupled with the iBiquity technology, gives regulators a way to support digital radio without the controversy that seems to come with any effort to reallocate portions of the broadcasting spectrum.

Yet some supporters of low-power community radio stations that serve college campuses, small towns and some urban neighborhoods say that the effects of the new technology on them could be devastating.

"The big guys will be trashing the signals of the little guys," said Christopher Maxwell, who is trying to create a low-power station in Richmond, Va. The problem, Mr. Maxwell said, is that by broadcasting digitally, stations will be filling more of the spectrum at the very edges of their allotted channels. That might make it harder for receivers to pick up weak signals from stations that cannot afford to invest tens of thousands of dollars in digital transmission equipment, he said. Mr. Maxwell maintains a Web site opposing the technology (www.digitaldisaster.org).

The ruling also worried nonprofit groups that use portions of the broadcast spectrum to read newspapers and books over the air to blind and disabled listeners. Millions of Americans receive the broadcasts, according to David W. Noble, head of the government affairs committee of the International Association of Audio Information Services. They are generally broadcast at the edges of the channels owned by public radio stations.

It is possible that a fully digital system may lead to big improvements in such "sideband" services, as they are known. But fears about interference will be heightened as long as stations are carrying both analog and digital signals.

The F.C.C. acknowledged that such issues existed and said it wanted to address them in proposals for a final digital broadcasting standard. For now, the industry has temporary permission to broadcast digitally on FM frequencies around the clock and in the daytime only on AM channels. IBiquity said that tests to establish proposed standards for AM digital broadcasting after sundown, when AM signals travel farther, would be finished by the end of the year.

Advocates of the technology say that digital broadcasting can improve FM broadcasts to CD-quality sound and AM broadcasts to FM quality. In addition, digital broadcasts are less likely to be disrupted by obstructions like buildings and hills.

The biggest advantage, though, is that digital transmission will eventually allow broadcasters to offer listeners a wide range of data services. For instance, listeners could receive information about an artist whose music is being played, customized traffic reports or data about discounts at stores in shopping centers they are approaching. Owners of digital radio receivers that are envisioned will also be able to set them to record, edit and replay programming, just as owners of technologies like TiVo do today with television.