The D.C. Council is set to vote today on a bill to legalize same-sex marriage in the District, setting in motion a process that seems likely to allow gay couples to get married in the shadow of a Capitol filled with dozens of Members dead-set against it.

The bill, introduced by D.C. Councilman David Catania (D), has the support of 11 of the 13 members of the council, virtually assuring its passage. With a second vote expected in the coming weeks, it could be on Congress’ doorstep by early next year.

But while Congress has 30 legislative days to review it, Republicans are pessimistic about their chances of preventing its implementation. Overturning the bill directly is almost impossible; it has been almost 20 years since Congress last struck down a D.C. bill using a resolution of disapproval. More likely is an attempt to slip language in the city’s annual budget that would block the marriages. Such steps have been taken in the past. For example, for years Congress prevented the city from enacting a needle-exchange program by prohibiting funding for it.

However, Congressional leaders are likely to keep the gay marriage issue off the floor. In the House, Majority Leader Steny Hoyer (D-Md.) is a staunch supporter of D.C.’s right to manage its own affairs, making the chances of floor action slim.

“We can try to strike funding or use some other creative way to address the issue,— said Rep. Jason Chaffetz (R-Utah), who has been outspoken about his opposition to the bill. “But it’s very difficult to deal with the 30-day time frame, especially given the fact that the Democrats have an iron grip on the process.—

Minority Leader John Boehner’s (R-Ohio) office was noncommittal, with spokesman Kevin Smith declining to discuss any plans to oppose the bill.

“Republicans believe that marriage is and should remain between a man and a woman,— he said in an e-mail, “and this is certainly an issue we continue to monitor closely.—

Chaffetz and other Congressional opponents have so far focused on stopping the bill at the city level, decrying the decision by the District of Columbia Board of Elections and Ethics to reject a proposal for a referendum on same-sex marriage. At a hearing earlier this month on two bills to give D.C. more autonomy, Chaffetz and Rep. Brian Bilbray (R-Calif.) told D.C. officials repeatedly that residents have the “right— to vote on the issue.

But the bill’s opponents might yet find a way to force a vote in Congress. Earlier this year, a bill to give D.C. its first-ever full House seat stalled when pro-gun Members attempted to attach an amendment to change D.C.’s gun laws. House leaders were unable to bring the bill to the floor without risking the attachment and passage of the amendment, mainly because of pressure from the National Rifle Association.

Similarly, conservative groups are sure to lobby Congress once the same-sex marriage bill makes it to the Hill. Ilir Zherka, executive director of the local group DC Vote, said his group and its coalition partners are already planning for that battle.

“We are bracing for at least some effort up on the Hill to try to undo what folks will do here locally on marriage equality,— he said. But until the bill’s Congressional opponents make a move, “it will be unclear on our side what we have to do.—

Congress’ response to the Jury and Marriage Amendment Act may offer some hint. The act, passed by the D.C. Council in May, requires the city to recognize same-sex marriages performed in other states. Its arrival in Congress was met with several opposition bills, but none made it very far. Rep. Paul Broun (R-Ga.) introduced a resolution of disapproval that gathered 37 sponsors, while Rep. Jim Jordan (R-Ohio) authored the DC Defense of Marriage Act. It so far has 59 sponsors, four of them Democrats.

Spokeswoman Meghan Snyder said Jordan has yet to decide how he’ll tackle the most recent bill. The bill’s language also isn’t final; D.C. officials rushed Monday to come to a compromise with the city’s Catholic archdiocese, which has threatened to cancel its social services if forced to recognize same-sex marriage.

“We’ll see how things play out,— Snyder said.