* Ryan seeks introduction to Americans
* Storm-tossed convention gets down to business
* Delegates keep wary eye on Hurricane Isaac
By Steve Holland
TAMPA, Fla., Aug 29 (Reuters) - Paul Ryan takes his turn in the spotlight on Wednesday for the biggest speech of his political career when he accepts the nomination as Mitt Romney's vice presidential running mate at the Republican National Convention.
With the convention shifting into high gear, delegates kept a wary eye on Hurricane Isaac as it pounded the Louisiana coast. There was concern that televised images of political revelry in Tampa, Florida, could provide a jarring contrast to the storm's onslaught.
Heading the list of speakers on Wednesday is Ryan, a conservative budget hawk from Wisconsin. That will set the stage for Romney's acceptance of his party's nomination on Thursday night, launching him into the final 10-week sprint of the election campaign.
Careful not to emulate predecessor Sarah Palin, who fell from grace quickly after bursting onto the 2008 campaign as John McCain's running mate, Ryan has made a cautious start to the presidential race.
It is still unclear whether he will help Romney draw support from undecided voters who may be the critical factor in the Nov. 6 election pitting the Republican ticket against President Barack Obama and Vice President Joe Biden. Polls show a mixed picture.
"Tonight, the American people -- millions who may not know a lot about Paul Ryan, other than the headlines that they've read -- are going to get to know Paul Ryan the way many of us know him: as a serious policy thinker," Republican U.S. Senator Marco Rubio told ABC's "Good Morning America" program on Wednesday.
Rubio, who represents swing state Florida and its many elderly residents, defended Ryan's controversial budget plan to cut government spending deeply and overhaul the government-run Medicare health insurance program for older Americans.
Ryan has energized conservatives in a way Romney was unable to do during the long months of the Republican primary battle, when he faced a number of conservative challengers.
The Obama campaign, hoping to steal some of Ryan's thunder, released an online video accusing him of harboring "out-of-step views from a bygone era" that would hurt the middle class, threaten Medicare and undercut women's abortion rights.
Despite criticisms of his budget plan, the boyish 42-year-old Ryan, a fitness fanatic, has shown himself to be an affable asset to Romney so far.
He has helped generate large crowds when the pair has campaigned together, and some conservatives who were not that excited about the former governor of Massachusetts are now ready to work hard for him with Ryan on the ticket.
Ryan also helps put in play Wisconsin, which has not voted for a Republican presidential candidate since Ronald Reagan in 1984. A Romney victory there could alter the electoral map in a way that could hurt Obama's hopes for re-election.
LITTLE KNOWN OUTSIDE WASHINGTON
Ryan's place in prime time on Wednesday offers him the chance to introduce himself to millions of Americans who are just starting to tune in to a presidential race that is too close to call with 70 days left until the voting.
While Ryan, chairman of the House of Representatives Budget Committee, is well known in Washington, he is little known elsewhere.
Democrats are portraying Ryan as a conservative ideologue whose budget proposal in the House would "end Medicare as we know it" and are using his budget plan against him in states like Florida, with its large population of retirees, and in Virginia, where thousands of government employees populate the suburbs adjoining the capital.
Romney can ill afford to lose either of those two states.
A Reuters/Ipsos poll on Tuesday found that exactly half of Americans approve of Ryan and the other half disapprove of him.
Speaking before Ryan will be Condoleezza Rice, who served as secretary of state under former Republican President George W. Bush. She is expected to take aim at Obama on foreign policy, which has taken a back seat to economic concerns, both at the convention and in the overall election campaign.
McCain, taking the podium in Wednesday's session, was also likely to critique Obama's record on the international stage.
"There is no doubt that the United States' voice has been muted. When the United States' voice is muted, the world is a more dangerous place," Rice told CBS' "This Morning" program when asked what Obama had done wrong in global affairs.
While Romney says Obama has weakened America's position in the world, the White House contends that the president has improved a U.S. image damaged by the Bush administration's perceived go-it-alone approach.
Rice told CBS she would not accept a position in Romney's administration if he won the election.
Other speakers at the Republican convention have sought to put a human face on the often robotic Romney and enhance his likability. On Tuesday, there was no better advocate for him than his wife, Ann Romney.
She admitted to reporters she had never used a prompting device to read a speech, but during the actual delivery she seemed at ease as she painted a personal portrait of Romney, who Democrats denounce as an out-of-touch wealthy elitist.
Mrs. Romney spoke of the early years of their marriage when the high school sweethearts dined on cheap meals of tuna and pasta, saying her husband was "not handed success" as Romney's opponents charge.
Rubio, who is scheduled to introduce Romney ahead of the Republican presidential nominee's speech on Thursday, said such soft details about Romney are unlikely to come from Ryan's remarks.
"If I know Paul Ryan, we're going to get a policies speech that's also inspiring," he told CBS.
Romney, who was on hand for his wife's speech, planned to deliver a speech to the American Legion in Indianapolis before returning to Tampa.