The California Supreme Court today blocked a scheduled Dec. 18 statewide vote on a Republican-drawn reapportionment plan that could have resulted in an unprecedented turnabout in the state's political power balance.

Republicans had hoped the reapportionment would ultimately remove several leading Democrats from Congress and return the California Legislature to GOP control.

All six Democratic appointees to the court voted to void the Dec. 18 ballot. The court's only Republican appointee dissented.

Republican officeholders immediately charged that the court, led by controversial Chief Justice Rose E. Bird, had rendered a political decision and that new initiatives would be necessary to thwart continued Democratic dominance.

Democrats and Republicans had been preparing for what was expected to be one of the bitterest political contests in the state's history.

The plan would redraw many of the long, twisting legislative and congressional districts that spread Democratic votes advantageously and helped give Democrats majorities of 28 to 17 in the state's delegation to Congress, 25 to 14 in the state Senate and 48 to 32 in the Assembly.

In the 1982 election, GOP congressional candidates received 48 percent of the vote but won only 37 percent of the seats.

If approved by the voters, the reapportionment could have forced several of the most powerful California Democrats in Congress to run against each other, including Henry A. Waxman, Anthony C. Beilenson, Howard L. Berman, Augustus F. Hawkins, Julian C. Dixon and Mel Levine.

More than 700,000 voters signed petitions to get the initiative, framed by State Assemblyman Don Sebastiani, on the ballot.

In an unusual, unsigned 36-page opinion, the court majority said the Sebastiani initiative violated a 76-year-old state constitutional rule allowing only one reapportionment per decade after each federal census.

Attorneys on both sides said the ruling cannot be appealed to the federal courts because it is based on the state, not the federal, constitution.

The court noted that Sebastiani felt that the people's will as expressed in an initiative took precedence over the "one-reapportionment-per-decade" rule, but it called this argument "novel in the history of this state."

Justice Frank Richardson, appointed by former governor Ronald Reagan, dissented, calling the decision a "defeat of the people's right to vote." The majority justices were Bird, Allen Broussard, Joseph Grodin, Otto Kaus and Cruz Reynoso, all appointed by former governor Edmund G. (Jerry) Brown Jr., and Stanley Mosk, appointed by former governor Edmund G. (Pat) Brown Sr.

Sebastiani, a Sonoma County Republican, said he planned to introduce a new initiative with the same reapportionment plan plus language removing the "one-reapportionment-per-decade" rule. In its decision, the court said he could do that.

Rep. David Dreier (R-Calif.), a supporter of Sebastiani, said he hoped the GOP would reintroduce a plan to give reapportionment powers to an "independent" commission, a proposal defeated in a statewide vote in 1982. Republican Gov. George Deukmejian made similar suggestions recently after rumors of an unfavorable Supreme Court decision began to spread.

State Attorney General John Van de Kamp, a Democrat, hailed the court's decision but said he expected further GOP attempts to circumvent it.