WEST PALM BEACH, Fla. — Governor Crist signed a bill yesterday moving Florida’s 2008 presidential primary up to January 29, leapfrogging several other states in a change that could dramatically alter the Republican and Democratic presidential nominating campaigns.

The move puts Florida’s primary, which had been scheduled for March, behind only the Iowa and Nevada caucuses and the New Hampshire primary and on the same day as South Carolina’s Democratic primary.

Florida has by far the largest population of any of the early voting states set for January and is the most expensive in which to campaign, giving well-funded candidates an even greater advantage and possibly drawing attention away from the smaller states.

“This is going to require the serious candidates to spend very, very large amounts of money and time in Florida,” a politics professor at Emory University in Atlanta, Merle Black, said. “If you can’t compete in Florida, that’s going to be a sign that you’re not a serious contender.”

Mr. Crist, a Republican, and other state GOP leaders have argued that Florida’s diversity and size merit more influence in deciding the nation’s leadership. The delegate-rich state decided the disputed 2000 presidential election. “We may not be the first in the nation, but we’re at the forefront,” Mr. Crist said after signing the bill. “We will be the first mega-state to weigh in on the next leader of the free world.”