A proposed ballot initiative that would ban gay marriage (search) passed a key hurdle Wednesday when the state attorney general ruled it would be permitted under a section of the state constitution allowing voters to overturn court decisions.

The action by Attorney General Tom Reilly (search), 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 (search) urged Reilly to certify the ballot question, saying voters "should not be denied meaningful participation in the legal definition of marriage."

Backers of the proposed referendum cite the Massachusetts Constitution's Article 48, which permits the people to petition for a constitutional amendment "that overrules a court decision when the court has declared a statute to be in violation of our constitution."

Gay marriage supporters had urged Reilly not to accept the proposed amendment, saying that Article 48 applied to court rulings overturning a statute, while the court case involving gay marriage rights did not overturn an existing law.

Gary Buseck, legal director of Gay and Lesbian Advocates and Defenders, which sued the state over gay marriage and won, said the group would challenge Reilly's decision.

The measure defining marriage as between a man and a woman had been proposed last month by the Massachusetts Family Institute. The state legislature is considering an alternate constitutional amendment that also would overturn gay marriage but would legalize Vermont-style civil unions.