UPDATE 3-US court won't reconsider Wal-Mart sex bias case

(Adds comment from plaintiffs' lawyer)

By Gina Keating

LOS ANGELES, Dec 11 (Reuters) - Wal-Mart Stores Inc (WMT.N) suffered a legal setback in its attempt to head off the biggest sexual discrimination case in U.S. history when an appeals court on Tuesday allowed the case to remain a class-action lawsuit.

The plaintiffs estimated they could win billions of dollars in lost pay and damages and that as many as 2 million women who have worked for Wal-Mart in its U.S. stores since 1998 could join the suit.

But the court left open the option for Wal-Mart to file a new petition for a rehearing, and Wal-Mart attorney Theodore Boutrous said the Bentonville, Arkansas-based retailer intends to do so.

The three-judge panel of 9th U.S. Circuit Court of Appeals said it would not reconsider its own decision affirming class certification to the case, but would allow both sides to appeal to the full court.

The revised ruling, which upholds a San Francisco U.S. District Court judge's finding on class certification, allows the parties to file new petitions for rehearing.

"The court's order makes clear that Wal-Mart can now file a new rehearing petition in light of the new opinion," Boutrous said.

Brad Seligman, a lawyer for Betty Dukes, the longtime Wal-Mart employee who brought the lawsuit in 2001, said in a statement that "the women at Wal-Mart are one step closer to their day in court."

Six other women have since joined the suit.

A three-judge panel ruled in a split decision in February that more than 1 million women could join a suit charging bias in pay and promotions. (Reporting by Gina Keating, editing by Mark Porter, Leslie Gevirtz, Richard Chang)