LAS VEGAS – A federal judge refused Thursday to shut down nine casino-based sites for Saturday’s caucuses, delivering a victory to Sen. Barack Obama in what has become an increasingly bitter Democratic contest here.

U.S. District Judge James Mahan rejected the argument that conducting some of the caucuses in casinos would give Obama an unfair advantage because he has been endorsed by the state culinary workers union, which employs thousands of casino workers. Siding with lawyers for the Democratic National Committee, he said federal law “recognizes the parties have the right to determine how to apportion delegates.”

The DNC, working with Nevada Democratic officials, approved the at-large precincts last summer to accommodate people who will be working when the hour-long caucuses are held at noon on Saturday. Any shift worker employed within a 2.5-mile radius of the Strip is allowed to participate, but those sites are expected to be dominated by culinary workers, many of whom are Latino. State party officials estimate casino caucusgoers could account for up to 10 percent of total turnout.

The lawsuit, brought by a state teachers union that has endorsed Sen. Hillary Rodham Clinton, has led to a nasty dispute between her campaign and Obama’s, escalating tensions just days after the two tried to defuse a racially tinged dispute.

The Clinton campaign has denied playing any formal role in the suit but has been critical of the casino caucuses.