John Stossel is stepping from broadcast to cable. It's a big move for Stossel and a telling move for TV, one more sign of how both broadcast and cable are changing.

Stossel, a longtime TV newsman and advocacy journalist, has left his post at ABC's 20/20 and gone to Fox News Channel and Fox Business Network. On FBN at 8 p.m. Thursday he starts a weekly one-hour program, Stossel.

Unlike anything on FBN, the show will feature guest panels - Yaron Brook of the Ayn Rand Institute, John Allison, chief executive officer of BB&T bank, Jerry Taylor of the Cato Institute, Superfreakonomics coauthor Stephen Dubner - and a live studio audience that Stossel will encourage to add its two cents' worth and more.

His multiyear contract also calls for frequent look-ins on Fox News during the day and prime time, as well as four business/consumer-themed one-hour specials during the year.

Speaking by phone from New York, Stossel says his move is a measure of the state of the broadcast audience (shrinking); the more open, entrepreneurial atmosphere at Fox; and the chance to do something different.

He joined 20/20 as a consumer-affairs reporter in 1981. His profile grew as his opinionated libertarian-flavored advocacy, running against the grain of traditional broadcast journalism, drew both wild adherents and wild detractors. He defined consumer affairs in an assertively broad way: global warming, health care, civil liberties, social security, free trade, anger management.

Fans said Stossel told truths no one else in the mainstream would touch. Detractors called him a crypto-rightwinger whose work was not journalism but polemic.

By 2003, he was coanchor of the venerable news show. He also did ABC specials, often controversial, sometimes acerbic, such as 1997's Junk Science: What You Know That May Not Be So or 2006's special on education, titled Stupid in America.

With consummate info-age savvy, Stossel grew the brand with John Stossel's Take, a much-followed Web site, and Stossel in the Classroom, a series of DVDs, streaming Web video programs, and teacher guides aimed at middle school, high school, and college students. "My audience in high schools," he says, "now outnumbers my audience when I left ABC."

Stossel has been a frequent guest on Fox News mainstays such as Hannity and Colmes and The O'Reilly Factor. Some industry observers felt a move to Fox was just a question of time. So why now?

"When people used to ask me, 'Why don't you go to Fox?' " Stossel says, "I used to say, 'Well, on 20/20 I get 15 million people watching and Fox gets under a million.' But that was years ago. By the time I left, 20/20 was down to five million, and a Fox leader like O'Reilly, on his best night, is close to that. And Fox does issues all the time on things I want to focus on, issues of economic liberty."

He joins a luminous trickle of former ABC news stars to Fox. Brit Hume jumped in 1997, Chris Wallace in 2003. Producer Michael Clemente, who worked with Stossel on 20/20, became senior VP of news at Fox last year.

"After 40 years of reporting," Stossel says, "I got more interested in economics and economic liberty, and there wasn't room for that at ABC. And Fox Business News has 24/7 opportunity for it. It's brand new and they have the airtime. I just called [Fox founder] Roger Ailes and said, 'I'm ready, hire me.' They offered me an hour a week to do a libertarian show. No one else has offered me that."

An hour show - that worried him at first. Could he keep up the pace and quality? "But I began to think about how I've been doing speeches at campus to students who hate liberty and explaining my viewpoint to them, and the exchange of opinions had been lively, so I thought I could do that on a show."

Stossel says he felt the difference between the established broadcast network and the newer, smaller, hungrier cable channel right away. "I've worked for all three traditional broadcasters," he says, "and the biggest difference I felt is, that at the networks, you'd have lots of meetings. Any time anyone had an idea, it was time for a big meeting. At Fox, you have an idea, and somebody likes it and you get to do it.

"Because it's nonunion, lots of people there are trying new things and experimenting. It's a very free environment."

Stossel does promise to be a departure for FBN, which specializes in on-the-fly reports and half-hour shows. A whole hour in prime time - already unusual. That tinderbox live audience - all but unheard of in the Fox cosmos. Each show will examine a single theme.

"It certainly feels unlike anything I've seen out there before," he says. "We're planning a whole show on [the Ayn Rand novel] Atlas Shrugged, and another one on global warming. I'm doing one on John Mackey, CEO of Whole Foods, on the consumer boycott against him." (Mackey's Wall Street Journal op-ed denying that Americans have an intrinsic right to health care sparked calls for a boycott.)

Stossel will also be news-driven. "I'm not starting with the Atlas Shrugged one because nobody would watch the second one," he says, chuckling. "In fact, it's still a little bit of a mystery what we're doing for the first one. If Obama makes news when he goes to [the United Nations Climate Change Conference in] Copenhagen, that will drive my show."

How does a libertarian feel these days, with government policy trending the other way, and calls flying for more, not less, regulation? Stossel agrees that embattled is a good term - "but also enraged. All I can do is do my stories and try to say what I've learned: how government controls don't work. I at least hope to show people that there is an alternative."

John Stossel gets his chance to do that starting Thursday on FBN. With its Stosselian focus, its special-a-week flavor, and the promise of vigorous give-and-take from a range of viewpoints, Stossel seems to suit Stossel, who happily calls it "both nerve-racking and exciting."

Contact John Timpane at 215-854-4406, jt@phillynews.com, or twitter.com/jtimpane.