BY ALFONSO CHARDY

U.S. Rep. Lincoln Diaz-Balart, a Republican admired by many Cuban exiles, has been reelected handily to the 21st Congressional District since it was created 15 years ago. Raul Martinez, a Democrat, was the popular Hialeah mayor of the majority Cuban-American city for almost a quarter century -- reelected even after a criminal conviction later reversed on appeal.

Both arrived in South Florida as children when their families fled after Fidel Castro's revolution in Cuba. But there the similarities end. Each man's personal style of communicating and the policies they embrace are markedly different.

With Raúl Castro's ascension Sunday to president of Cuba, U.S. policy toward the communist-run island is expected to play a key role in the race between those two men and contests involving two other South Florida Cuban Americans in Congress -- Reps. Mario Diaz-Balart and Ileana Ros-Lehtinen.

Generational change and the rise of independent voters will be tested most in the 21st district, which stretches from Miramar and Pembrokes Pines in Broward County to Miami Lakes, Hialeah, Doral and Kendall in Miami-Dade County.

Martinez, 58, is counting on both, coupled with his long history of winning elections in Hialeah, to help him take the district. He plans to focus, too, on differences in domestic policy, such as healthcare reform.

Diaz-Balart, 53, is counting on his tested years in Congress -- bringing hundreds of millions of dollars to the district for healthcare research and U.S. security and to exile-run democracy projects for Cuba, among other things. He is banking, too, on the loyalty of older, hard-line exile ''supervoters'' to keep him in office.

As for leadership style, each man views the other's strength as a potential negative. The scion of a prominent political family, Diaz-Balart can sometimes seem autocratic in his demeanor and his rhetoric. Martinez, for his part, proudly proclaims his blue-collar roots, which at times in his career have shown him to be more street scrabbler than statesman.

Now that Raúl Castro is officially leading Cuba -- although Fidel has not stepped down as chief of the island's Communist Party -- the three South Florida congressional contests will also have to grapple with the negotiations question.

Diaz-Balart and the two other Cuban-American Republicans in the U.S. House have made it clear that there can be no negotiations until Cuba's leadership releases all political prisoners and allows a free press and labor unions and multiparty elections. Those conditions have been codified into U.S. law.

Negotiating any deal with Raúl Castro is out of the question for the incumbents.

Lincoln Diaz-Balart noted in a statement last week when Fidel Castro announced his resignation as president that "as of this time, there has been no change in totalitarian Cuba.''

Martinez offers some wiggle room.

He would not touch the 4-decades-old embargo but says he would push Congress to lift the travel and money restrictions imposed by the Bush administration in 2004 -- a reflection of a generational split in the Cuban-American community, according to several polls.

As for negotiating with Cuba under the current leadership, Martinez says, "I don't see myself leading the way. I would like to be at the table if the United States government is going to do it, to make sure that the interests of the Cuban people in Cuba and the Cuban people in exile are protected.''

The contest is drawing national attention because if Martinez defeats Diaz-Balart, the outcome could have consequences beyond district boundaries if Democrats keep control of the House.

''Overall, the Democrats are trying to broaden the playing field and pull more races into play than ever,'' said Nathan Gonzales, political editor of the respected Rothenberg Political Report, a nonpartisan newsletter in Washington, D.C. "This race falls into that category.''

Gonzales said the strategy also involves targeting two other historically safe districts in South Florida -- Mario Diaz-Balart now faces Miami-Dade Democratic Party chief Joe Garcia, a member of the moderate Cuban American National Foundation, and Ros-Lehtinen is facing Colombia-born businesswoman and political neophyte Annette Taddeo.

''The Democrats are hoping there is a shift within [Lincoln's] district, but there is no evidence yet that such a shift is taking place,'' Gonzales said.

In a recent telephone interview, Diaz-Balart said that if the Martinez camp wants to turn the campaign into a ''referendum'' on the Cuba issue, so be it. ''I accept the referendum challenge on whatever issue,'' he said.

The race against Martinez may ultimately resemble the one in 2002 involving his brother Mario, Diaz-Balart said, if the Martinez camp claims that the Cuban community is tilting against sanctions.

''It's deja vu all over again, in the words of Yogi Berra, the great philosopher,'' he said, pointing to his brother's win in 2002 in a race in which Cuba policy played prominently.

Diaz-Balart maintains that easing the travel restrictions on Cuban exiles would open the door to lifting the ban on travel to Cuba, sending millions of U.S. dollars to prop up the Castro government.

''The U.S. tourism ban, which is the most important aspect of the embargo, would simply become unsustainable,'' Diaz-Balart said. "How could I ask my colleagues [in Congress] from other states to continue prohibiting travel to Cuba by their constituents if I were advocating unrestricted travel to Cuba for Cuban Americans?''

One Florida International University survey released last April showed that 64 percent of 1,000 Cuban Americans -- including nonvoters -- in Miami-Dade said they would like to return to pre-2004 travel rules.

But a September 2006 poll whose results Diaz-Balart recently gave to The Miami Herald showed that 85.2 percent of Cuban-American voters in his district favor maintaining the limits.

The Latino National Survey, by the University of Washington, shows a more nuanced reaction by exiles and first-generation Cuban Americans in Florida. A plurality, 43 percent of respondents, disagreed with the travel restrictions. But those who agreed or didn't care exceeded the number of those who disagreed -- respectively, 35.9 percent and 20.7 percent.

Martinez supporters believe that he can energize Democrats and independents who are interested more in healthcare and bread-and-butter issues than in Cuba policy and bring to his camp some Hialeah Republicans who supported him as mayor.

''Raul represents high energy, high performance, a new direction for the congressional district and the priorities of the Congress,'' said former Florida Democratic Sen. Bob Graham, who backs Martinez.

Former Florida Republican Party chairman Al Cardenas counters that Martinez has little chance of winning because of past legal troubles and because district voters have historically sided with Republican candidates.

Martinez was indicted in 1990 and later convicted of extortion and racketeering in zoning deals -- but an appeals court overturned the verdict, and two subsequent trials ended in hung juries. Federal prosecutors then dropped the case.

''Every time you have to explain why there was a conviction and what happened, that's a negative,'' Cardenas said. "And in that particular district, voters have voted overwhelmingly for Republican candidates across the board, not just Lincoln, but for president and senator.''

The 21st district has 124,744 Republicans and 101,267 Democrats. The numbers reflect a decline of 4,558 Republicans and a slight gain of 111 Democrats since the 2006 election. More significant, perhaps, is an increase of unaffiliated voters to 71,208.

Miami Herald staff writer Laura Figueroa contributed to this report.