The action by Attorney General Tom Reilly, a Democrat who is expected to run for governor in 2006, clears the way for conservative groups to begin the long process of gathering signatures and lobbying lawmakers in hopes of putting the issue before voters in 2008.
Supporters now must go out and gather the signatures of at least 65,825 Massachusetts voters. If they are successful, the question then must by approved by 25 percent of two successive sittings of the 200-member state Legislature. The question would then be placed before voters again as a constitutional amendment in 2008.
The state's highest court ruled in 2003 that it was unconstitutional for the state to ban marriages between gays and lesbians. The following spring, the nation's first state-sanctioned same-sex marriages began taking place in Massachusetts and thousands of gay couples have since tied the knot.
In a letter last week, Gov. Mitt Romney urged Reilly to certify the ballot question, saying voters "should not be denied meaningful participation in the legal definition of marriage."
On Tuesday, California lawmakers became the first in the country to approve a bill allowing same-sex marriages.
The legislation could still be vetoed by Gov. Arnold Schwarzenegger, who has expressed an acceptance of gay marriages but said it was an issue that should be decided by voters or the courts.
"He will uphold whatever the court decides," spokeswoman Margita Thompson said Tuesday after the state Assembly approved the same-sex marriage measure, 41-35. The Senate approved it last week.
A state appellate court is considering appeals of a lower court ruling that overturned California laws banning recognition of gay marriages. And opponents of same-sex marriage are trying to qualify initiatives for the 2006 ballot that would amend the state Constitution to ban gay marriages.
The bill's supporters compared the legislation to earlier civil rights campaigns, including efforts to eradicate slavery and give women the right to vote.