SEMINOLE, Florida (Reuters) - President Barack Obama kicked off a two-day bus tour of the key election battleground state of Florida on Saturday with former Florida Governor Charlie Crist, who endorsed Obama's 2008 rival John McCain but has since left the Republican Party.

Trying to build on the momentum of this week's Democratic National Convention and overcome another tough jobs report, Obama is spending the weekend canvassing a state that he and his Republican opponent, Mitt Romney, both want to win in order to achieve victory in the November 6 U.S. election.

The Democratic incumbent hopes Crist, a once popular Republican governor, will help Obama appeal to political independents, who are likely to determine the victor in the state.

"We have a leader with a cool head, and his name is President Barack Obama," Crist told the crowd of some 11,000 at an outdoor rally.

"He is working hard for the middle class. He is working hard for Florida," Crist said.

Crist campaigned for Republican presidential nominee McCain in 2008 but left the Republican Party in 2010 when polling suggested he would lose the Republican nomination for U.S. Senate to Marco Rubio, a favorite of the conservative Tea Party movement. Crist ran as an independent and Rubio won in a three-way race.

Crist embraced Obama - literally - as the president campaigned for his economic stimulus bill in 2009, giving him a big hug that was videotaped and replayed endlessly. It reinforced Republican suspicions that Crist was not a true conservative.

Obama, with sleeves rolled up and no tie, embraced Crist again on Saturday after his remarks.

"I want to thank Charlie Crist for his introduction, for his support, for showing that the values that we're fighting for are not Democratic values or Republican values, they are American values," Obama said.

'ROMNEY DON'T CARE'

Obama has traveled to Florida 10 times so far this year, according to his campaign. Obama used his stop on Saturday to criticize Romney and his running mate, congressman Paul Ryan, for their opposition to his 2010 healthcare law and proposals to reform Medicare, the popular government health insurance program for the elderly.

"By the way, Florida, you should know I will never turn Medicare into a voucher system," he said. "No American should have to spend their golden years at the mercy of insurance companies."

Ryan proposed a plan two years ago that would transform Medicare into a program in which recipients would use vouchers to buy private insurance.

Romney has also pledged to repeal the healthcare law often called "Obamacare." Obama told the crowd the former Massachusetts governor's plan should be called "Romney don't care" and joked that Republicans believed tax cuts were so important they could help a person's love life.

Romney's campaign kept up the heat on the president over his economic record. Government data on Friday showed that U.S. employers added a lower-than-expected 96,000 jobs in August.

"After a disastrous convention week and a widely panned speech that was short on specifics, President Obama delivered more empty promises and false attacks today in Florida," said Romney spokesman Ryan Williams.

"As yesterday's dismal jobs report showed - and as President Obama admitted - job creation in America isn't good enough, yet he didn't lay out any new ideas for getting our economy back on track."

Brian Olinger, 40, who attended the president's rally, said Crist could help Obama in Florida. "Even though I was a Democrat, he did some good things for teachers and other people when he was governor," he said.

(Twitter: @jeffmason1; Additional reporting by Jane Sutton; Editing by Will Dunham)

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