But Miller said O'Malley's efforts to use a ballot issue to broker a budget deal should have been his last resort, only if the votes for a slots bill couldn't be nailed down.
House Speaker Michael E. Busch said there's "more of an openness" among legislators for putting the issue on the ballot than for voting for a slots bill.
A constitutional amendment would restrict the sites and number of machines, Busch said.
Asked if a statewide issue would resolve the slots debate, Busch said it could.
"If people vote no, then they didn't want it. That's pretty easy," the Anne Arundel Democrat said.
The governor has not decided whether to ask legislators to put the slots issue on the ballot, said O'Malley spokesman Rick Abbruzzese. It's "too early" to say whether O'Malley would campaign in favor of a constitutional amendment legalizing slots, Abbruzzese added.
Aaron Meisner, chairman of Stop Slots Maryland Now, said a referendum won't relieve the "fatigue" that legislators and Marylanders have with the slots debate.
"The worst part is if the referendum is defeated, Magna and Penn National and all of those other companies will be back in Annapolis the very following January to talk about the same thing all over again," he said.
Still, a referendum would give O'Malley and legislators "an escape route from what looks to be a very controversial issue," said Matthew A. Crenson, a political science professor at the Johns Hopkins University.
The idea of letting voters decide is "a hard argument to resist and I think one that is going to prevail in the end, especially if it has provisions to allow counties or cities to opt out."
If the issue does go before voters, Crenson said, "The gaming industry is going to descend on Maryland like locusts. But [for] the people who don't want slots, no amount of advertising is going to persuade them. Others are likely to say 'Yes, but not in my backyard.'"
Sun reporter James Drew contributed to this article.