Dr Laura doesn't do tea and sympathy. For 30 years, she has been dispensing tough love to tens of thousands of listeners who call her radio talk show each day, seeking blunt, provocative and unashamedly conservative advice on how to cope with their most pressing personal problems.

"So what?" she likes to tell victims of childhood abuse. "You're still responsible for your actions!" To a pregnant woman wondering whether to agree to her boyfriend's request for an abortion, she once declared: "You got knocked up by a guy who wants to kill your child? Get a backbone transplant here!"

The inflammatory rhetoric has helped to turn Dr Laura Schlessinger, to use her full name, into America's most successful female radio host, with a fortune estimated at US$100 million ($140 million) and a weekday audience of 10 million loyal listeners, spread across 200 radio stations.

This week, however, it also cost Schlessinger her job. The so-called Queen of Hate Radio announced that she had decided to quit the airwaves amid controversy over her repeated use of the word "n****r" during an episode of her three-hour-long programme.

Trouble began last Wednesday, when an African-American woman, who was married to a white man, called Schlessinger's studio asking for advice on dealing with friends of her husband who have fallen into the habit of making racist comments to her.

Schlessinger, who counts mixed-race marriages as one of the many things she generally disapproves of, told the woman she was being "hypersensitive", and added that she shouldn't automatically take offence at racial taunts, even if they contained the word "n****r".

"Black guys use it all the time," she declared. "Turn on HBO, listen to a black comic, and all you hear is 'n****r, n****r, n****r'. I don't get it. If anybody without enough melanin says it, it's a horrible thing; but when black people say it, it's affectionate. It's very confusing."

The caller became audibly upset, saying that she had been "caught back" by Schlessinger's use of "the 'n' word". To which the host replied: "I'll say it again: n****r, n****r n****r ... If you're that hypersensitive about colour, and don't have a sense of humour, then don't marry out of your race."

The provocative tone was vintage Schlessinger. (Her famous quotations include "Feminists nauseate and sicken me. They've destroyed the sanctity of motherhood.") But that didn't stop her use of the 'n' word from sparking national media attention and fierce criticism from race relations activists.

She swiftly apologised, interrupting her programme the next day to say that she "did the wrong thing".

But critics, noting that Schlessinger had used the apparently verboten word "n****r" a total of 11 times in the short conversation, were unimpressed and began calling for advertisers to boycott her show.

On Tuesday, Schlessinger, who has written dozens of bestselling self-help books with (now ironic-sounding) titles such as Ten Stupid Things Women Do To Mess Up Their Lives, declared defeat. "My contract is up for my radio show at the end of the year and I've made the decision not to do radio any more," she said, in a surprise appearance on Larry King's CNN show.

"I want to regain my first amendment rights," she said. "I want to be able to say what's in my heart, and on my mind, what I think is helpful and useful, without somebody getting angry, some special interest group deciding this is a time to silence a voice of dissent."

The affair has highlighted the excesses of so-called "shock jocks", who are ubiquitous on the United States airwaves, and whose freewheeling enunciation of conservative values has been one of the key factors in the rise of the so-called "tea party", a right-wing populist movement loosely connected to the Republican Party.

For Schlessinger, the third most popular shock jock in the nation, it was also part of an ugly trend. A decade ago, gay rights groups forced her to apologise for calling homosexuality a "biological error", and claiming that allowing same-sex couples to adopt would put children in the hands of paedophiles, since "a huge portion of the male homosexual populace is predatory on young boys".

Her TV chat show was cancelled after just six months, following a campaign by gay rights activists, who convinced more than 170 advertisers to boycott it.

In future, Schlessinger told Larry King, she will make a living from her internet site, podcasts, and occasional YouTube clips. She believes online forums will make it harder for her to be targeted by "angry, hateful groups that don't want to debate. They want to eliminate."

* Explaining why she doesn't approve of test-tube babies:
"When you're the product of some fellow ejaculating into a cup for $100 there isn't the same sense of history."

* On relationships:
"I use the term 'unpaid whore' for women who shack up with guys, rather than dignify themselves and sexual intimacy with a marital commitment. I tell them that at the very least, they ought to be paid for sex, since it ultimately means nothing profoundly important to him past the orgasm."

- Independent