California Republican Gov. George Deukmejian today announced a Dec. 13 special election for a new state reapportionment plan that is expected to set off one of the most bitter and expensive political campaigns in the state's history.

California Democratic Party leaders said they would challenge the special election in court.

They also had threatened to hold their presidential primary on the same date as the special election, for which Republicans traditionally have a bigger turnout, in the hope of attracting more Democrats and defeating the reapportionment plan.

But after a two-hour joint caucus of state senate and assembly Democrats in Sacramento tonight, state senate president pro tem David A. Roberti said the legislators had overwhelmingly voted to discard the early primary idea.

Many legislators apparently feared that the early primary, which would have violated national Democratic Party rules, would have led to a damaging intraparty fight that could have resulted in the California delegation being ousted from the 1984 national convention.

An early primary also would have severely disrupted strategies and finances of several of the major Democratic presidential hopefuls, who had not expected to campaign in the nation's most populous state until late spring.

Democrats called the special election a plot by ultraconservative Republicans to slip through a redistricting plan favorable to the GOP at a time when many people would not go to the polls.

"We don't want to sanctify a Christmas election," said Roberti, referring to complaints that the December date would discourage voting because of the holiday season.

The new redistricting plan would create enough safe Republican and closely contested districts to threaten the Democrats' control of the legislature and their majority in the congressional delegation.

The dispute over the proposed redistricting already has helped delay appoval of a state budget for a record 18 days, and things could get worse. Judging from the bitterness and outrage expressed towards Deukmejian by Democrats today, the special election announcement does not appear to have helped efforts to compromise in the budget fight. Thousands of state workers have missed paychecks, and unemployment recipients have been paid only through court order.

The Republican redistricting plan, according to some analysts, would give the GOP a chance of capturing 41 of the 80 assembly seats by the end of the decade, bringing to an end the Democrats' lengthy hold on California's legislature and the reign of assembly speaker Willie Brown, the state's most powerful Democratic leader.

State Democratic Chairman Peter Kelly estimated that the party would have to spend more than $5 million to defeat the reapportionment in the special election, and many analysts expected the Republicans would spend even more to pass it.

National party rules require that all presidential primaries and caucuses be held between March 13 and June 12, except for New Hampshire and Iowa, which were granted waivers to hold their events March 6 and Feb. 28, respectively, to ensure that they remain first.

National Democratic leaders, however, threatened not to seat any delegates selected in violation of these national party rules, which by a decision of the U.S. Supreme Court take precedence over state laws.

Although several Republican strategists here see the reapportionment measure as a political godsend, it was less warmly received when first proposed by Don Sebastiani, a Republican state assemblyman who is a member of a wealthy wine-growing family.

California Republicans were angry with the way the legislature's Democratic majority carved up the congressional districts two years ago, which broke up growing suburban pockets of GOP strength and widened the Democrats' 21-to-20 advantage to 28 to 17.

But Democrats also had protected the districts of most Republican incumbents, and Sebastiani had to raise money on his own to collect signatures for his radical redistricting plan. It removed the worst of the twisting, odd-shaped districts designed by Democrats, ended the legislative splitting of many cities and counties and greatly increased Republican chances in future elections.

In announcing the special election, Deukmejian noted that under current law and recent court decisions voters had to rule on the new plan before the scheduled June, 1984, primary or the Democratic-drawn boundaries would remain until the 1990 census.

The election squabble has become tightly entwined in the politics of the state's drawn-out budget battle.

Democratic legislators, asking for about $600 million more than Deukmejian says he is willing to spend, criticize him for authorizing a special election that may cost the state $14 million to $17 million to administer.

Deukmejian suggested today that the legislature could save money by amending the election code so it could schedule the special election Nov. 8, when some local elections already are scheduled.