LOS ANGELES — Democrats were trying to build their biggest majorities in years Tuesday as voters filled 100 seats in the California Legislature.

Democrats were targeting six Assembly seats now held by Republicans — enough to give them the two-thirds majority needed to approve state budgets, tax increases and constitutional amendments and to override gubernatorial vetoes.

Republicans were trying to hold on to those seats and pick up a hotly contested San Joaquin Valley district where the termed-out Democratic incumbent was backing the GOP candidate.

In the state Senate, the fight centered on two districts, one held by a termed-out Democrat and the other by a termed-out Republican. Democratic victories in both those races would put them within one vote of the two-thirds majority.

Democrats now hold 48 of the Assembly’s 80 seats and 25 of the Senate’s 40 seats. They need to get to 54 in the Assembly and 27 in the Assembly to be able to put together two-thirds majorities without Republican help.

It’s been 30 years since Democrats have had a two-thirds majority in the Assembly and 43 years since they’ve held that much power in the Senate. They last had as many as 26 Senate seats in 2002.

In Northern California, Democrats Alyson Huber, a Lodi attorney, Joan Buchanan, a San Ramon school board member and John Eisenhut, a Turlock almond grower, were seeking Assembly seats now held by termed-out Republicans.

In Southern California, Democrats Marty Block, the president of the San Diego Community College board, and Manuel Perez, a Coachella Valley school board member, were running for soon-to-be-open GOP Assembly seats.

And Democrats were hoping that San Fernando Valley high school teacher Ferial Masry could upset Assemblywoman Audra Strickland, R-Thousand Oaks, in another race receiving significant funding from the Democratic Party.

The only Democratic Assembly district in any real danger of changing parties was in the southern San Joaquin Valley, where termed-out Assemblywoman Nicole Parra, D-Hanford, was supporting her former Republican challenger, retired California Highway Patrol officer Danny Gilmore. Gilmore was running against Shafter City Councilwoman Fran Florez, the mother of Parra’s bitter rival, Sen. Dean Florez, D-Shafter.

One of the hottest Senate races pitted Assemblyman Greg Aghazarian, R-Stockton, against Assemblywoman Lois Wolk, D-Davis, for the seat now held by termed-out Democrat Mike Machado, D-Linden.

In the other, former Assemblywoman Hannah-Beth Jackson, a Democrat from Santa Barbara, faced former Assemblyman Tony Stickland, a Thousand Oaks Republican, for the seat held by Sen. Tom McClintock, R-Thousand Oaks.

The nine hottest races attracted more than $45.7 million. That included $10.2 million in independent expenditures by groups representing employers, teachers, attorneys, nurses and others.