by Sasha Issenberg

ST. PAUL - When Rachel Maddow arrived at a local café one morning last week on behalf of the Air America affiliate that broadcasts her three-hour drive-time show in the Twin Cities, she was dressed for radio, with a loose-fitting V-neck T-shirt and thick-rimmed black glasses.

One of the hundreds of listeners who patiently waited in line to meet Maddow came with an offering: a "Give Peace a Chance" lapel pin that she hoped Maddow would sport on her MSNBC television show. "I won't wear jewelry" on the air, Maddow said, apologetically affixing the pin to a corner of her shirt, near her waist. "I don't want to start a cascade of things I can't control."

It may be too late to stop the gush. Maddow was part of the original lineup on Air America, founded in 2004 to counter conservative dominance of talk radio under the market-friendly promise that liberals, too, could be entertaining. More than anyone else, Maddow fulfilled that pledge, with an affable and erudite approach to the day's news and the rhetorical combat that inevitably surrounds it.

Tonight, "The Rachel Maddow Show" debuts on MSNBC, leaving her on the cusp of full-blown stardom in the mainstream media that her most devoted fans see as an enemy.

Maddow, 35, was an accidental radio personality. She got her start on Holyoke's WRNX-FM only after winning a tryout to be a morning-show sidekick; Maddow had moved to the Pioneer Valley after college to pursue a career in AIDS policy, and still spends every weekend there, prizing the Massachusetts fishing license that allows her to catch trout near her Northampton-area home.

She brings a studied ambivalence about her newfound TV fame, which has come thanks to steady appearances as an MSNBC pundit. (The glasses usually are left behind.) Maddow has not owned a television since leaving home at 17, and she spends more time describing how she will defend her new program from the medium than taking advantage of its possibilities.

"The strategy is to make it as much as possible reflective of who I am, and avoid the homogenizing tendencies of TV production," she said. "It's like being put through a meat grinder and coming out as a pasteurized and homogenized meat product. I want to remain a veal chop."

Since auditioning in 2005 for a role as a sidekick to Tucker Carlson on his since-canceled afternoon show, Maddow has become a key face of the new, feisty, ratings-boosted MSNBC.

"MSNBC is trying to define a niche for itself as a center for commentary," said Sid Bedingfield, a former CNN executive who teaches journalism at the University of South Carolina. "It wants to be the home for liberal and left-wing viewers."

Much of that has been propelled by the ratings success of Keith Olbermann, whose nightly show gleefully attacks Republicans, rarely with counterpoint. Maddow was a frequent substitute host for Olbermann on his "Countdown" show, and he pushed MSNBC executives to give her the slot between his 8 p.m. broadcast and a replay at 10 p.m. (The two now share an agent.)

"With Keith Olbermann, TV finally figured out, like a lot of the radio industry, that talk for the left is economically successful," said Janet Robert, owner of KTNF, the Minneapolis-area Air America affiliate.

While critics increasingly call the network a Fox News of the left, an MSNBC executive said the network had not made a conscious decision to hire liberal talent, but was not bothered if efforts to alter its style had left it ideologically imbalanced.

"I look at the MSNBC brand as high-powered intellects," said Bill Wolff, a vice president for prime-time programming. "I'm not saying we're NPR, but there is an appetite for really smart discussion of the news. That's more about what I'm trying to make Rachel's show about than her position on a particular issue. I don't think you have to agree with Rachel in your views to really enjoy Rachel."

Although she happily holds up the liberal position in left-right debates, Maddow prides herself on being "cripplingly patriotic" - she signs radio-station bumper stickers "Your Country Needs You, xox" - and, the daughter of an Air Force captain, she has a yen for national-security issues.

The former Rhodes scholar, with a doctorate in political science from Oxford, is writing a book about military politics in postwar America and is famous at MSNBC for bringing a scholarly rigor to her preshow research and preparation. She has been known to arrive at Rockefeller Center from her Manhattan apartment nine hours before she is due to go on air, cloistering herself in a cubicle with an iPod as she reads and writes on the day's news.

"One of the things that separates Rachel from many people is the amount of fresh information she brings to her storytelling," said Wolff. "She really often isn't expressing an opinion as much as laying out facts that lead to the conclusion."

When Maddow took questions at the St. Paul cafe, it was clear her fans saw no limits to her potential expertise: Would Sarah Palin withdraw? How concerned was Maddow about voter fraud? Does human nature include an instinct for compassion?

"I'm not a biologist," Maddow cautioned. "But I think that we're naturally empathetic."

Maddow, who came out as a lesbian as a teenager, says that one of the galvanizing moments in her political development was Pat Buchanan's declaration of a "cultural war" at the 1992 Republican convention. Now the two are frequently used as good-humored, left-right sparring partners on MSNBC. Maddow praises Buchanan as a "gentleman."

"Pat enjoys debating, and I enjoy debating," Maddow told her fans in St. Paul. "When Pat is saying something outrageous, you know when you yell at the TV? I get to yell at him in person. I get to yell at the TV and it hears me."

As a host, Maddow says, she expects to continue debating on her show, but only as part of a broader repertoire of reported pieces, interviews, and commentaries. "I won't be Punch and Judy. I'm not into the fight for the sake of the fight. If it's not illuminating to present two sides of an issue, I don't want to," she said.

Maddow said she was particularly looking forward to taking on subjects of personal fascination - Kurdish politics and the failures of American infrastructure - that she says do not get covered enough. She wants to have debates on same-sex marriage and the need for more troops in Afghanistan, where the presidential candidates did not necessarily disagree in predictable ways.

"Where's the left and right on that?" she said. "Let's hash it out."