(adds background on law and political campaign in Florida)

By Bill Cotterell

TALLAHASSEE, Florida, June 9 (Reuters) - Florida Governor Rick Scott, who promised a crackdown on illegal immigration four years ago, signed legislation Monday allowing children whose parents came to the United States illegally to pay in-state tuition at Florida colleges.

Earlier efforts to extend in-state tuition rates to undocumented students at public colleges and universities had failed, with opposition from leading Republicans. It passed this spring as party leaders try to appeal to Hispanic voters in an election year.

Scott, a Republican seeking re-election who previously opposed the measure, skirted the issue of illegal immigration in a news release that focused instead on tuition costs.

"Signing this historic legislation today will keep tuition low, and allow all students who grew up in Florida to have the same access to affordable higher education," he said.

The new law applies to undocumented students who attended a Florida school for at least three years. In-state tuition is about one-fourth the rate charged for non-Floridians.

Currently, 17 other states have provisions allowing for in-state tuition rates for undocumented students, according to an analysis by the Florida House of Representatives.

Scott timed his approval of the bill to coincide with the start of a weeklong "college affordability" tour of major Florida cities, as he seeks to emphasize his differences with his main rival in November, Charlie Crist.

The state Republican Party released an ad blasting Crist, a former Republican governor now running as a Democrat, for allowing universities to hike tuition by up to 15 percent a year under his watch.

Crist's campaign issued a statement praising the tuition break but labeling it a bald political ploy intended to shore up Scott's relations with Florida's growing Hispanic voting population.

"In a remarkable turnaround, Governor Rick Scott went from fierce anti-immigrant to finally accepting the reality of Florida," said Senate Minority Leader Chris Smith, a Democrat from Fort Lauderdale. "Young people who were brought here by immigrant parents deserve a chance at affordable higher education."

Scott set a hardline immigration tone in his 2010 race, promising to copy Arizona's law permitting police to demand proof of citizenship from anyone they suspect of being in the country illegally. Scott also vetoed a bill that would have allowed driving licenses for immigrants whose deportation had been stayed.

Although conservative Cuban-Americans usually vote Republican, a Quinnipiac University poll in March showed Crist leading Scott among Hispanic voters. (Additional reporting By Letitia Stein in Tampa; Editing by David Adams and Doina Chiacu)