Boston ? A proposed ballot initiative that would ban gay marriage 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 Atty. Gen. 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.