The state's seven justices will hear three hours of oral arguments on the issue Tuesday, The Sacramento Bee reported Monday.

"This will be one of the -- if not the -- legal landmarks in the struggle for equal rights," said Geoffrey Kors of Equality California, which supports gay marriage. "It will have a ripple effect not only in this country, but the whole world."

Only one state, Massachusetts, allows gays to marry. Connecticut, New Jersey and Vermont have civil unions.

A part of the court's consideration is Proposition 22, the voter-approved initiative in 2000 that limited marriage to a man and woman.

"The justices can destroy or protect marriage. If the justices alter the definition of marriage, then the people will certainly override them at the ballot box," said Randy Thomasson, president of the Campaign for Children and Families.

The state Supreme Court will hear the case after years of legal wrangling following a San Francisco judge's ruling that California's ban on gay marriage was unconstitutional, the newspaper reported.

In 2006, a state appeals court reversed that decision and upheld the ban on same-sex marriage.