The three-pronged battle over which state Senate districts will be used for this year's elections is reaching a climax that will determine whether Democrats can achieve a two-thirds majority in the upper legislative house.

The state redistricting commission released maps for Senate, Assembly and congressional districts last August. It immediately became evident that with a little luck, Democrats could gain two seats in the 40-member Senate, thus reaching the two-thirds threshold and empowering them to pass tax bills without Republican support.

Republicans filed suit to block the Senate maps, only to be rebuffed by the state Supreme Court, but also launched a signature drive to challenge them via referendum.

Were the referendum to qualify, the Supreme Court would decide which maps to use for 20 Senate elections this year – the commission's versions, the previous districts or court-devised ones.

The commission's maps also are under scrutiny of the U.S. Justice Department for compliance with the Voting Rights Act, with a decision due by next week unless the department seeks more time.

The referendum's signatures are being verified, but since a sample count has not indicated definitively that it will qualify, a full tally is being ordered and that will take about six weeks to complete.

Meanwhile, the contenders – Republicans on one side and Secretary of State Debra Bowen and the redistricting commission on the other – sent lawyers to the Supreme Court Tuesday to argue over whether the court should consider alternative maps for 2012 and if so, which maps they should use.

Lawyers for Bowen and the commission argued that if the court needs to act because the referendum is likely to qualify, it should use the commission's maps.

"It's too late to start redrawing lines," Bowen's attorney, George Waters, told justices. "There's no second set of districts here that I'm aware of," the commission's lawyer, James Brosnahan, added.

But Republican attorney Charles Bell suggested that the old districts "with modification" could be used in 2012, or the court could create new Senate maps by combining the commission's 80 Assembly districts into 40 Senate districts.

From justices' questioning, it appears they are poised to act but are in a quandary on which districts to use if need be.

Meanwhile, it's still uncertain whether the Justice Department will give its approval to the commission's Senate maps, which have been criticized for diminishing Latinos' chances of electing senators.

Any major changes ordered by either the Justice Department or the Supreme Court that improve Latino prospects could also undermine Democrats' hopes of achieving a two-thirds majority – the real stakes in this complex process.

© Copyright The Sacramento Bee. All rights reserved.

Call The Bee's Dan Walters, (916) 321-1195. Back columns, www.sacbee.com/ walters. Follow him on Twitter @WaltersBee.

• Read more articles by Dan Walters