The Supreme Court agreed yesterday to decide whether California may require employers to provide special benefits for pregnant workers.

A savings and loan association challenged the California law on the grounds that it conflicts with the federal Pregnancy Discrimination Act of 1978, which it said mandates that pregnancy be treated like every other disability.

The savings institution was joined by an unusual coalition of groups, including the Reagan administration, the National Organization for Women, the American Civil Liberties Union and the U.S. Chamber of Commerce.

Women's groups have argued against such preferential treatment, fearing that it would make employers reluctant to hire women of child-bearing age.

The California law requires that up to four months of disability leave must be offered to pregnant employes. When a receptionist took a four-month leave for pregnancy, the California Federal Savings and Loan Association denied her request for reinstatement.

State officials then filed a complaint on her behalf alleging that Cal Fed had violated state law.

The 9th U.S. Circuit Court of Appeals last April said the federal law was only a minimal "floor beneath which pregnancy disability benefits may not drop -- not a ceiling above which they may not rise."

Cal Fed is arguing in California Federal Savings and Loan Association v. Guerra that the federal law prohibits discrimination either in favor of or against pregnant workers.

The court also agreed to hear three election law cases, including one that could lead to changes nationwide in how primary elections are conducted.

A federal appeals court last year struck down a Connecticut law that said only voters who are members of a political party may vote in that party's primary.

The appeals court said such closed primary laws, similar to those in 38 states, unconstitutionally conflicted with the First Amendment rights of party members to freedom of association.

Connecticut's Republicans, badly outnumbered by Democrats and hoping to expand their base, passed a rule that independent voters also could vote in certain primary elections. The Democratic-controlled state legislature refused to amend the state law, and the Republicans sued.

The state, joined by 15 others, asked the high court to overturn the ruling in Tashjian v. Republican Party of Connecticut.

In a second election case (Monro v. Socialist Workers Party), the court agreed to review the constitutionality of a Washington state requirement that minor parties achieve a minimum level of support to earn a slot on the general ballot.

And in another case, the court said it would hear an appeal by the Federal Election Commission that a Massachusetts antiabortion group improperly used its funds -- as opposed to those of a separate political action committee -- in an election flyer listing candidates' votes on abortion.

An appeals court ruled that federal election laws could not require "ideological" groups to set up separate entities. The case is FEC v. Massachusetts Citizens for Life Inc.