As a practical matter that means a resolution would have to be approved this year or next, and then approved again by the General Assembly taking office in 2011 after the next election. That means the soonest the issue could go on the ballot is 2012.
If it isn't approved this year or next, the earliest voters could weigh in would be 2014.
Gov. Chet Culver has said only that he is studying the decision along with legal advisers. Spokesman Phil Roeder said the governor will likely have more to say on the issue, though the timing was uncertain.
Roeder acknowledged Culver was getting pressure on the issue from supporters and opponents.
"We're getting a bunch of phone calls and e-mails," said Roeder. "It's kind of split. It's been constant all day."
Legislative leaders are struggling to end this year's session by next week, and Gronstal's position virtually rules out any action on gay marriage this year. Lawmakers will likely face pressure from social conservatives when they convene next year.
Veteran Republican political strategist David Roederer said it's the longer term that could cause some headaches for Democrats who control both the Legislature and the governor's office.
"Long term it's going have a big impact in a couple of ways," said Roederer. "The last thing most legislators want is people paying attention to what goes on at the Capitol."
The gay marriage debate, he said, has focused that attention tightly on the workings of the Legislature, on an issue that both critics and backers feel passionately about, Roederer said.