Many Americans tune in each day to so-called "talk radio" stations to learn what's happening in U.S. politics, and what the host of each program has to say about it. This week, a new talk radio network premiered in some communities, offering a pointedly liberal perspective on the issues of the day.

Evan Cohen, the chairman of America's newest talk radio network, Air America, knows how popular that kind of format can be. "Political talk radio for the last 25 years has been a very strong, viable economic business," he says. "And we're just tweaking the model a little bit."

Evan Cohen is doing a little more than "tweak the model" with his new company, Air America Radio. He's trying to stand the model on its head. Talk radio has been dominated by outspoken and entertaining conservative commentators like Rush Limbaugh and Bill O'Reilly. Air America began broadcasting this week with a round-the-clock schedule of liberal program hosts. They are sharply critical of the White House, as they make fun of their conservative competition and invite prominent liberals to join them on the air.

With the White House and Congress controlled by Republicans, the hosts of the new network, including comedian Al Franken, actress Janeane Garofolo and rapper Chuck D, find themselves in the same position conservative commentators say they were in during the Democratic administration of Bill Clinton, as Michael Harrison of the trade publication Talkers Magazine explained to NBC.

"People who were of the conservative mindset felt that, 'Hey, the whole deck is stacked against us. This form of radio really is the only place we can go to get our point of view,'" he said.

They built rightwing radio into a powerful influence across America. Rush Limbaugh's program, for example, is heard on nearly 600 radio stations. Air America has only five stations, plus a satellite radio channel and streaming audio on the Internet. And there may be a bigger obstacle to the new network: being entertaining enough to attract a following.

Conservative radio talk-show host Michael Reagan told NBC that listeners will tune to people like him because liberals, he says, tend to have views that are "too nuanced" to be sufficiently provocative.

"They listen to us because we're not boring. And liberal radio tells you to be boring, if you will," he said.

Leftwing politicians who have tried hosting radio programs in the past, including former New York Governor Mario Cuomo and onetime California Governor Jerry Brown, didn't last long. Air America is hoping that it will fare better with a staff of entertainers, not politicians. And one conservative talk show host sees some possibilities in the new lineup. G. Gordon Liddy phoned Al Franken's first show on Wednesday, and the conversation was heard on both programs:

Liddy: No matter what the political orientation of the program, may be, the fact is, it has to entertain the listener, and you have a long history of being a very successful entertainer.
Franken: I hate everything you stand for.
Liddy: I know that, and vice versa. But that doesn't mean we can't be friends and have a good time together.

Later this month, Air America will begin broadcasting in San Francisco, as well as New York, Los Angeles, Chicago and two other cities. Executives say they have enough funding to operate for several years without having to make a profit.