Republican vice presidential pick Sarah Palin has accused Democratic nominee Barack Obama of using the theme of "change" merely as a slogan to promote his political career.

"Here's how I look at the choice Americans face in this election," the Alaska Governor said on Wednesday in excerpts of her speech to the Republican National Convention.

"In politics, there are some candidates who use change to promote their careers. And then there are those, like John McCain, who use their careers to promote change."

Palin also defended her credentials to serve as vice president, saying she had entered grass roots local politics to improve the lives of her kids and then worked her way up the executive ladder.

"Before I became Governor of the great state of Alaska, I was Mayor of my hometown, and since our opponents in this presidential election seem to look down on that experience, let me explain to them what the job involves," Palin said in the excerpts.

"I guess a small-town mayor is sort of like a community organiser' except that you have actual responsibilities." That was another swipe at Obama, as the Democratic nominee worked as a community organiser in Chicago after law school.

Palin also lashed out at the media, which she blamed for fanning a clutch of controversies which have dogged her since Republican presumptive nominee McCain named her as his running mate last week.

"I'm not a member of the permanent political establishment and I've learned quickly, these past few days, that if you're not a member in good standing of the Washington elite, then some in the media consider a candidate unqualified for that reason alone."