JEFFERSON CITY, Mo. (AP) – Missouri voters overwhelmingly approved a constitutional amendment Tuesday to ban gay marriage, the first such vote since the historic ruling in Massachusetts last year that legalized same-sex weddings there.

Although the ban was widely expected to pass in conservative Missouri, experts said the campaign served as a key barometer for which strategies work as the gay marriage battle spreads to ballot boxes around the nation.

At least nine other states, and perhaps as many as 12, will vote on similar amendments this year.

The amendment had garnered 74 percent of the vote with 42 percent of precincts reporting.

Missouri and 37 other states already have laws defining marriage as only between a man and a woman. But amendment supporters fear a court could toss aside the state law, and they believe the state would be on firmer legal ground if an outright ban is part of the Constitution.

“I’m very gratified and encouraged and thankful that the people of this state understand our current policy’s a wise public policy and they want to see it protected from a legal challenge,” said Vicky Hartzler, a spokeswoman for the Coalition to Protect Marriage in Missouri.

Opponents said the amendment was unnecessary and discriminatory, but knew they faced an uphill battle in Missouri.

“We’re already reaching out to these other states, sharing with them what we learned, what worked, what didn’t work, and we’ll move on,” said Doug Gray, campaign manager for the Constitution Defense League. “Ultimately we’re right and they’re simply wrong.”

Louisiana residents are to vote on a marriage amendment Sept. 18. Then Arkansas, Georgia, Kentucky, Mississippi, Montana, Oklahoma, Oregon and Utah are to vote on the issue Nov. 2. Initiatives are pending in Michigan, North Dakota and Ohio.

Four states already have similar amendments.

AP-ES-08-03-04 2358EDT