SAN FRANCISCO — A conservative legal group asked the California Supreme Court yesterday to put off finalization of its decision legalizing same-sex marriage until voters got a chance to weigh in.

The Arizona-based Alliance Defense Fund wants the ruling stayed until November, when voters will probably encounter a ballot measure that would amend the state constitution to ban gay marriage. That amendment would overturn the justices’ ruling.

In court papers submitted late yesterday, the group warned that the state would suffer “great public harm and mischief” if it began allowing same-sex marriages on June 16, when the court’s decision would ordinarily become final.

Defense Fund attorneys also said implementing the ruling in the meantime would be an unnecessary expense for the state and cause unneeded confusion for couples.

“Permitting this decision to take effect immediately — in light of the realistic possibility that the people of California might amend their constitution to reaffirm marriage as the union of one man and one woman — risks legal havoc and uncertainty of immeasurable magnitude,” the attorneys wrote in the petition.

Many couples started planning weddings and making appointments to secure marriage licenses immediately after the justices overturned the state’s gay marriage ban on May 15.

A cloud of uncertainty lingers over the pending unions, however. A coalition of religious and social conservative groups is in the process of putting a measure on the November ballot that would write a gay marriage ban into the state constitution.

County clerks have until June 18 to verify the signatures needed to qualify the amendment for the election, according to the Defense Fund. A preliminary count by 37 counties indicates that the initiative has a high chance of being put to voters, the group said in its petition.

Defense Fund attorneys asked the Supreme Court to hold a hearing on when its decision should take effect or to amend it to prevent it from being implemented for now.