BY BETH REINHARD

Barack Obama turned Saturday afternoon at Miami-Dade County Auditorium into Sunday morning at church, falling into a call-and-response rhythm with his Democratic flock and urging them to have faith in a young, black newcomer to Washington.

Obama addressed about 1,500 people, the largest South Florida crowd so far in the 2008 presidential race and one of the most diverse.

''I'm asking Miami-Dade to believe in this campaign,'' said the Illinois senator, standing in front of an American flag some 20 feet high. "I'm asking you, Miami-Dade, to believe in yourself.''

Many of Obama's comments echoed previous speeches, but he kept straying from the teleprompters when the audience led him. His approach lent the speech an intimacy and spontaneity rarely seen on the campaign trail.

''I love you back, baby,'' he responded to a supporter without missing a beat. He agreed when someone raised the specter of Haiti after he decried injustice in Cuba. And he reacted to another man who voiced frustration with President Bush.

''I'm sick and tired of the administration treating the Constitution as a nuisance to be negotiated around instead of as the foundation of our democracy,'' he said, and when the audience responded with a standing ovation, he added, "You don't like it, either.''

The speech in Little Havana capped a week in which Cuba was thrust to the forefront of the presidential race. In a column published Tuesday in The Miami Herald, Obama called for ''unrestricted rights'' on Cuban-American travel and remittances to the island.

The Bush administration limits Cuban Americans to visiting their relatives once every three years and sending $100 per month as part of an effort to squeeze Fidel Castro's repressive regime. But Obama said Cuban Americans can deliver a message of freedom and help foster financial independence from Castro. He said he would continue the trade embargo.

''You have my word -- and the government and people of Cuba should hear my call -- that our cause is simple,'' he said. "It's what drew my father across an ocean, and many of you across the waters to our south. That principle is libertad. Until there is justice in Cuba, there is no justice anywhere.''

Democratic rival Hillary Clinton's campaign has said she would only lift travel restrictions in limited cases until Castro falls.

The crackdown on travel and remittances is a flash point in a Cuban-American community torn between wanting to deprive Castro's economy and yearning to support loved ones.

For about 25 protesters across the street from the auditorium -- who held signs that said, ''Obama -- Castro's fundraiser'' -- ending the restrictions is tantamount to propping up a communist dictator. Cuba's foreign minister last week praised Obama's stance, infuriating hard-line exiles.

But for some of the Cuban Americans in the audience, Obama's demand makes sense.

''The damage that we would do is far less than the good Cuban Americans would do by spreading their ideas and principles,'' said Jorge Dominicis, a politically well-connected sugar executive. "Among a certain element, any sign of change is met with great resistance.''

Obama delivered his speech in the same auditorium where Ronald Reagan stirred a Republican crowd more than two decades ago. ''Can you imagine, in the heart of Little Havana?'' cried Miami-Dade Democratic Party Chairman Joe Garcia, who organized the event, looking out into the packed auditorium.

Obama touched on the traditional Democratic agenda of affordable healthcare and better and higher wages, but didn't wade too far into policy details. He also demanded that the United States address global warming and the civil war in Darfur. The freshman senator who touted his ''two decades of public service outside of Washington'' kept returning to his theme that Americans are crying out for change.

''They want someone new,'' he said. "They want to turn the page. They want to write a new chapter of American history.''

That sentiment appealed to Audrey Brown of Edgewater, who was clutching Obama's autobiography. ''He's a fresh voice in the crowd,'' she said.

Obama took a few shots at Bush and at Clinton, without mentioning her name. She has a commanding lead in the Florida polls.

''No one had the judgment to ask the tough questions before we sent our troops to fight,'' he said, alluding to the New York senator's vote authorizing Bush to go to war.

The speech in Little Havana capped a week in which Cuba was thrust to the forefront of the presidential race.

Obama's 45-minute speech was packed between spirited performances by the Miami Northwestern High marching band and gospel choir. It came near the end of a two-day swing through Florida that took him from the historically black Florida A&M University campus in Tallahassee to the Democratic stronghold of Broward County to the trendy Mansion club on South Beach.

The party was one of 20 around the nation for a group of young donors and voters the campaign has dubbed Generation Obama. Students paid $25; others paid $100 and up.

Robert James, 37, a deputy with the Broward Sheriff's office, wanted to see Obama in person. ''You don't get very much off TV,'' he said.

While Obama is slated to return to Florida next month, his campaign is expected to invest only a fraction of the time and money it is putting into other states with early primaries. Just hours before he spoke, the national Democratic Party said Florida's decision to move up its presidential primary to Jan. 29 would cost it all of its delegates to the 2008 convention.

In an interview with The Miami Herald, Obama pledged to campaign in Florida but acknowledged that the state's officially worthless primary was a "consideration.''

He did not mention the party sanctions in his speech, where former U.S. Rep. Carrie Meek, the matriarch of Miami's black political establishment, sat in the front row.

''What has God wrought,'' she said, "it's beyond my wildest dreams.''

Miami Herald staff writers Jennifer Mooney and Nicholas Spangler contributed to this report.