A measure to place a constitutional ban on gay marriage on the fall ballot was narrowly voted down in the state Senate on Wednesday, but the referendum could still come back for a revote in the final days of the legislative session.

The failure of the measure was largely blamed on the absence of Sen. Karen Johnson, R-Mesa, who missed a planned vote a week ago and is on vacation this week.

Johnson said in a memo to her Republican colleagues that she would try to return Friday to vote on the measure. Republican lawmakers and conservative groups were already launching efforts to pressure her to make sure she returns, but it's not certain whether the measure will be reconsidered on Friday.

The vote Tuesday, which would have sent the measure to the ballot if it had been successful, was part of a several months-long odyssey to get a constitutional amendment on the fall ballot defining marriage as the union of one man and one woman. The measure seemed like a sure thing when it was introduced in February, but it struggled to get out of the House after several false starts and it languished for many months without being put to a vote in the Senate.

On the floor Tuesday, supporters said voters should have the right to decide whether to ban gay marriage in the constitution and cited the recent court decision in California legalizing gay marriage there as a reason to move forward.

"We are going to have homosexual couples from Arizona go to California to get married and come back to Arizona and challenge our state law," said Sen. Ron Gould, R-Lake Havasu City.

Opponents argued the measure is unnecessary and called it a waste of time as the Legislature struggles to finalize a budget for the fiscal year that begins next week. Gay marriage is illegal under state law, and state courts have upheld that law.

Democratic Sen. Paula Aboud said she doesn't believe this is the kind of bill that constituents in Arizona want lawmakers working on. "They want us to work on things that impact life in the state," Aboud said.

In 2006, Arizona voters became the first in the nation to defeat a ballot initiative banning gay marriage. It also would have barred governments from offering benefits to domestic partners of employees, gay or straight.