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The first decision in what is expected to be a long legal battle over California’s same-sex marriage ban will be announced Wednesday afternoon, with both sides planning appeals if they lose.

The California Supreme Court ruled 4 to 3 that gays and lesbians were entitled to marry under the state Constitution in a historic ruling in May 2008. Voters passed Proposition 8 six months later, amending the state Constitution to ban same-sex marriage.

The decision will be posted online between 1 p.m. and 3 p.m., Pacific time, and will be written by Chief Judge Vaughn R. Walker of Federal District Court here, who oversaw a lengthy trial on the ban — Proposition 8 — this year. Walker, an appointee of President George H.W. Bush, heard myriad witnesses testify about the history of marriage, the nature of homosexuality and the degree of power gays and lesbians possess in the political system during the 2 1/2-week trial in January. (previous story)

But on Tuesday, supporters of the ban — who were widely regarded as being on the defensive at many points in the trial — had already filed paperwork indicating that they would appeal, according to The San Francisco Chronicle.

The trial, which included testimony from experts on marriage, sociology and politics, was instigated by a lawsuit filed by two gay couples who said that Proposition 8 impinged on their constitutional rights to equal protection and due process. The proposition was passed in 2008 by 52 percent of California voters, and nullified an earlier decision by the state Supreme Court allowing same-sex marriage.

Regardless of the outcome, supporters of gay marriage were planning demonstrations in San Francisco and Los Angeles on Wednesday evening.