St Paul, Minnesota - Alaska Governor Sarah Palin painted herself as a reformist Washington outsider in a rousing primetime address to introduce herself as Republican presidential candidate John McCain's running mate.

When Palin finished Wednesday, McCain made a surprise appearance on the Republican Party's convention stage ahead of his own speech Thursday to accept the centre-right party's nomination for US president.

"Don't you think we made the right choice for the next vice president of the United States?" McCain asked after greeting Palin's entire family - her husband, their five children and their prospective son-in-law - on stage in St Paul, Minnesota.

Palin forcefully answered concerns about her experience after two years as governor of the vast, sparsely populated state, taking sharp aim at Democratic presidential nominee Barack Obama and the media - as did many of the speakers on the night.

"I'm not a member of the permanent political establishment," Palin said. "Here's a little news flash for all those reporters and commentators: I'm not going to Washington to seek their good opinion - I'm going to Washington to serve the people of this great country."

After her speech, 2,380 national convention delegates formally nominated McCain and Palin as the Republican standardbearers.

Palin, 44, a self-described hockey mom, lends a working-class background and youthful enthusiasm to the Republican ticket in a possible counter to Obama's charisma.

Wearing a simple string of pearls and her already iconic, slightly up hairdo, Palin brought a touch of Marge Simpson, the maternal organizer of the Simpsons cartoon series.

Her unusual speaking tone lacked the trained drone of most politicians and was reminiscent of the smiling but relentless police chief Marge Gunderson in the 1996 movie Fargo, a role that earned actress Frances McDormand an Oscar.

Michael Bayham, a delegate from Louisiana, called Palin "a new voice in the crowd with a very distinct Alaskan accent, ... someone who's got thick skin but who's also telegenic."

Brian Summers, a Republican strategist, said Palin "hit it out of the park" in her speech.

Palin has a record of clashing with Alaska's Republican establishment, having defeated party incumbents to become both mayor of her small Alaska town and later state governor.

The McCain-Palin ticket's potential to shake up and reform Washington was a recurring theme Wednesday as were the party's prescriptions to revive a sluggish US economy and reduce the country's dependence on imported oil.

Former presidential candidate Mitt Romney, who made a fortune as a venture-capital investor before entering politics, labelled Democrats as big spenders who supported government intervention and would squelch American ingenuity.

Other speakers continued on the convention theme of McCain, 72, a US senator from Arizona, as a proven leader in a dangerous world, while painting first-term Senator Obama, 47, as a risky, inexperienced choice.

Democrats at their own convention last week in Denver, Colorado, argued that Obama had shown judgement that McCain lacked and framed McCain as a loyal follower of the unpopular policies of President George W Bush.

Palin was a six-year mayor before being elected governor in 2006 on a reformist agenda. She was little-known outside her remote home state before being named Friday as McCain's unexpected choice for the vice presidential slot, and the choice sparked debate about Palin's inexperience.

Palin argued that Obama's message of change could not compare to McCain's own legislative record or even her own record of reform in Alaska.

"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," she said.

Palin becomes only the second woman on a US major-party national ticket. Obama chose Delaware Senator Joe Biden, a leading voice on foreign policy, as his running mate.

Carl Toepel, a Republican delegate from Wisconsin, praised Palin's "dynamic" address and suggested she would hold her own in a vice presidential debate against Biden, a former prosecutor.

"She'll be able to shake up Washington," Toepel said.

McCain, long considered a maverick within his own party, seems to have solidified his support among the conservative Republican base with the choice of Palin. The mother of five, including a boy born this spring with Down syndrome, has a strong track record of opposing abortion.

But her policies on reproductive issues, including opposition to sex education in public schools, have been in high focus since Monday when Palin and her husband announced that their 17-year-old daughter, Bristol, was pregnant and planning to marry the teenage father of the unborn child. The young couple sat with the rest of the Palin family Wednesday at the convention.

Hawaii Governor Linda Lingle, recounting Palin's life, mentioned her 20-year marriage with "five beautiful children and a grandchild on the way." The convention crowd applauded, and one woman in the stands rose to wave a sign proclaiming "pro-life, pro-Palin."