RICHMOND -- A majority of Virginians support a proposed state constitutional amendment affirming Virginia's ban on same-sex marriages and civil unions, according to a poll conducted for The Roanoke Times and other Virginia newspapers.

The amendment has the support of 56 percent of the voters who participated in a statewide survey by Mason-Dixon Polling & Research. Advocates of the amendment said the poll reflects widespread support for the constitutional change. But opponents argued that the numbers suggest they are gaining ground in their effort to defeat the measure.

The results come from a telephone survey of 635 registered voters conducted Tuesday through Thursday. The poll has a margin of error of plus or minus 4 percentage points.

The proposed amendment has become an emotional and contentious issue, fueling vigorous campaigns by organizations on both sides of the debate. Supporters consider the amendment necessary to protect Virginia's ban on same-sex marriages from court challenges. Opponents have raised a variety of objections to the measure, with some contending that the amendment reaches beyond marriage to prohibit certain legal arrangements between unmarried partners.

The poll indicates that the amendment has its strongest support in Southwest Virginia, where 64 percent said they intend to vote for it. Opposition to the amendment is strongest in Northern Virginia, where 48 percent said they plan to vote against it and 44 percent said they will support it.

"We're confident that Virginians are going to join the other 20 states that have passed marriage amendments," said Chris Freund, a spokesman for va4marriage.org, a group pushing for passage of the amendment.

Claire Guthrie-Gastanaga, the campaign manager for a coalition trying to defeat the amendment, argued that the 18-point gap between supporters and opponents would have been closer if the poll question matched the one that will appear on the Nov. 7 ballot.

In the poll, participants were asked how they will vote on a constitutional amendment stating, "That only a union between one man and one woman may be a marriage valid in or recognized by this Commonwealth and its political subdivisions."

The poll did not include the additional sentences on the ballot question, which deal with prohibitions of civil unions and other legal arrangements between unmarried partners.

Gastanaga said that portion of the amendment is vague and could drive down support for the amendment.

"All it takes to drive the numbers down below 50 is for voters to read the actual language," she said.

Gastanaga cited a poll commissioned by her organization, the Commonwealth Coalition (www.votenova.org), in which the entire text of the ballot question was posed to voters. That survey, conducted in June, showed 45 percent favoring the amendment, 40 percent opposing it and 14 percent undecided.

The Mason-Dixon Virginia Poll also gauged opinions on two other proposed constitutional amendments. Voters are divided on an amendment that would delete the state constitution's ban on the incorporation of churches. The provision is obsolete because a federal court ruled that it violates the U.S. Constitution. Just 32 percent said they support the change and 30 percent said they oppose it, with the remainder undecided.

By a margin of 47-24, voters indicated support for another amendment that would allow localities to grant partial real estate tax exemptions for new construction and renovations in conservation, redevelopment or rehabilitation areas.