MADISON, Wis. -- A new statewide poll gives supporters of a state constitutional amendment defining marriage a narrow advantage.

But both sides are optimistic about the poll results and see a path to victory in November.

According to the WISC-TV-sponsored survey, 48 percent of those polled said that they would vote for the amendment if the November election were held today. About 40 percent oppose the measure and 12 percent said that they are undecided.

The telephone poll randomly called 600 likely voters over a three-day period from Aug. 14 to 16. The margin of error in the survey is 4 percent. Besides the marriage amendment, the poll also asked questions about the races for governor and attorney general.

University of Wisconsin-Madison political science professor Charles Franklin said the race has all the markings of being one of the closest battles over a gay marriage amendment in the country.

Supporters of the amendment have been hitting the state and county fair circuit, while the opposition is now running 10 offices around the state of Wisconsin.

One of those offices is operating out of a prominent store front on Madison's highly traveled State Street. What was once retail space is now a crowded space filled with computer terminals and a dozen volunteers, WISC-TV reported.

Staff at the State Street office believe that without their efforts, the constitutional amendment would be getting overwhelming support in the polls.

"I think what we're seeing is people who initially started as a 'yes' vote now are moving to undecided, and I think they're going to keep moving to no," said Michael Tate, Fair Wisconsin campaign director, in response to the poll.

But Julaine Appling, executive director of the Family Research Institute of Wisconsin, is also optimistic about the poll results.

"You know, the undecided vote is something you have to pay attention to. But I think as we continue to talk about this, that number will go much more in our favor," Appling said.

Anti-gay marriage videos have been sent to churches around the state, WISC-TV reported.

Political scientists believe the first part of the amendment question on the November ballot is pretty straightforward in its language about marriage being between one man and one woman.

Franklin said that he believes the second question is open for interpretation and will be the key for the amendment's success come November.

The second part of the question talks about banning legal status for couples engaged in anything "substantially similar" to marriage.

"If voters see this as a vote on gay marriage, it will probably pass by a substantial margin. If they see it as an intrusion into contracts and other kinds of benefits on unmarried, but heterosexual people, then support is going to go down quite a bit," Franklin said.

Appling said that the amendment is about the definition of marriage, not benefits.

"People are understanding this is about redefining marriage. It's not about benefits. It's not about discrimination. It's about whether or not we want the definition of marriage to be something other than one man and one woman," Appling said.

But Tate thinks voters will be wary of the far-reaching effects the amendment might have.

"The more voters find out about the far-reaching effects of this amendment -- how it would permanently prevent Wisconsin from ever offering civil unions, jeopardize domestic partner benefits and a whole host of other things ... we think that bodes really well for our campaign," Tate said.

Both sides are predicting a decisive victory when the battle hits the ballot box in November.