In the days leading up to Tuesday's election, support for a proposed state constitutional ban on gay marriage remains strong, with 63 percent voter approval, according to a new statewide poll of registered voters.

Amendment 3 would define marriage as the union of "a man and a woman" and prevent any other "domestic union" from being "recognized as a marriage or given the same or substantially equivalent legal effect."

Those who said they would vote against Amendment 3 comprised 32 percent of the 1,228 registered voters polled in the new Deseret Morning News/KSL-TV poll, conducted by Dan Jones & Associates.

Only 5 percent of voters remained undecided in the poll, with an error margin of 2.8 percent.

The poll, conducted Oct. 21-28, showed little change from previous surveys on the issue, but there was a spike in support, from 61 percent to 69 percent, in the final two days of polling.

It's telling, Jones said, that religious support is strongest among those who identified themselves as "very active" LDS — 82 percent of whom said they would vote for the amendment. "The thing about active LDS — they vote," Jones said.

The majority of Catholics, Protestants and "not active" LDS, meanwhile, said they oppose the amendment.

Support was divided along party lines — 83 percent of Republicans favored the amendment, while 71 percent of Democrats opposed it.

Among independent voters, 50 percent supported the measure, 44 percent opposed it, and 5 percent were undecided.

Scott McCoy, campaign manager of the Don't Amend Alliance campaign trying to defeat Amendment 3, remains optimistic despite the poll results, noting "there's a few wild cards out there.

"The ultimate poll is on election day," McCoy said. "I think we have good chance of surprising a lot of people."

Quin Monson, assistant political science professor at Brigham Young University, said Don't Amend's efforts have been well-organized and well-funded, but its message is "just a hard sell in this state."

Supporters have said Amendment 3 would simply define marriage and prevent so-called marriage substitutes such as civil unions.

Don't Amend has raised doubts about the amendment's legal implications, saying it "goes too far." The campaign said Amendment 3 would likely have adverse effects on existing legal benefits for unmarried partners, such as wills and powers of attorney, and could make some statutes, such as common law marriage, invalid.

Opponents also got the support of GOP Attorney Gen. Mark Shurtleff and his challengers Democrat Greg Skordas and Libertarian Andrew McCollough, who issued a joint statement opposing the measure.