The Senate Republican leadership is aiming for a mid-July vote on a constitutional amendment that would ban gay marriage, forcing Democrats to take a stand on the controversial topic just before the party heads to Boston for its presidential nominating convention.

Senate Republican Conference Chairman Rick Santorum (Pa.) said the GOP leadership is not yet prepared to officially announce a date, but he confirmed that GOP leaders are scouting for a July vote.

“We are sort of running the traps on this right now, and sort of seeing what kind of response we are getting,” Santorum said following Tuesday’s Republican Policy luncheon. “We are talking about it. I think there are a couple of meetings to be had yet before any official announcement is made.”

The issue was not broached with all 51 Republican Senators at the Tuesday meeting, but a handful of senior Senators and leaders “discussed the issue at length” Monday night, several GOP Senators and aides said. Unanimity about whether the GOP should pursue the issue in this election year did not emerge in that meeting, but a strong majority within the Republican Conference seems to favor at least forcing a vote.

“I think it needs to come up, and we need to vote on it one way or another,” said Senate Judiciary Chairman Orrin Hatch (R-Utah).

Socially conservative groups have been pressuring the Republican-controlled Congress to hold a vote on the issue this year, prompted in part by the May decision by Massachusetts to sanction gay marriages. Some Republicans hope that the decision to move up the vote to July would help inoculate the GOP from Democratic charges that the party is trying to play politics with an issue right before an election.

“We want to make sure we are as clear as possible that this is not a political exercise but an issue of substance,” said a GOP aide who requested anonymity.

But by scheduling the vote before the Democratic presidential convention, it could force some Democrats to vote against, or publicly state their opposition to, an issue that is championed by the gay and lesbian community, which is a key Democratic-leaning voting bloc.

The presumptive Democratic presidential nominee, Sen. John Kerry (Mass.), and Senate Minority Leader Tom Daschle (S.D.) are among those who have already stated publicly that they oppose gay marriage. Democrats are defending five open seats in the South, which is traditionally a conservative region of the country.

Santorum would not say if he has the 67 votes needed to amend the Constitution, but he suggested that voters should have an opportunity to know where incumbent candidates and challengers side on this issue.

“Our feeling is this is a legitimate attempt to address a foundational issue in this country,” he said.

Sen. Edward Kennedy (D-Mass.) said opponents of the constitutional amendment would vigorously dispute efforts to and vowed to “deal with whatever they serve up.

“I strongly believe that we shouldn’t write discrimination or prejudice into the Constitution,” he said. “It is not necessary to amend the Constitution, and we should not amend it.”

The House Republican leadership has not offered a time frame when that chamber would address the issue.

A spokeswoman for the Human Rights Campaign — a leading advocacy group for gay, lesbian, bisexual and transgender interests — said they are confident that an amendment will fall short.

“I think it doesn’t matter when they bring it up,” the spokeswoman said. “We think enough Senators will view this as an unnecessary” and as something that will undermine the Constitution.

Sen. Trent Lott (R-Miss.), who attended the Monday meeting, said he always understood that Senate Majority Leader Bill Frist (R-Tenn.) was “committed [to] having a vote on this in July for quite some time.”

But Lott warned that there is a chance the Senate might not actually vote on the merits of the bill itself, but rather a procedural vote to begin debate on the issue. Lott said such a situation was “not ideal, but it may be the only shot we get.”

The White House has already gone on record saying that it supports the constitutional amendment. In May, it urged Congress “to pass, and to send to the states for ratification, an amendment to our Constitution defining and protecting marriage as a union of a man and a woman as husband and wife.”

Still, resistance is expected from several moderate Republicans, including Sen. Lincoln Chafee (R.I.), who opposes the GOP leadership’s efforts to push the constitutional amendment through Congress. In May, Chafee told Roll Call that people should “come to grips with homosexuality.

“And once you have done that — [once you] cross that threshold of saying, ‘This exists’ — then better human nature should come out. With all the talk of freedom, freedom, freedom in every sentence by the administration, here is the chance to do something to show they mean it,” Chafee said.

For several months, Senate Republicans have been laying the groundwork for such a vote, issuing talking points to GOP Senators prior to the Memorial Day recess to help promote the party’s position on the issue.

“This is a national crisis that requires a national response — a federal constitutional amendment,” reads one of the talking points issued by Santorum, who is charged with helping to craft the Republican message.

In addition to putting potential pressure on Democrats, a July vote will also boost socially conservative groups, such as the Christian Coalition, that are eager to include the vote in its presidential and Congressional voting guides.