Monday evening’s preliminary test vote on the Employment Non-Discrimination Act essentially guarantees that the most consequential civil rights bill of the year will pass the Senate with genuinely bipartisan support, very likely by the end of the week.

And so, even before the crucial 60th public supporter was locked down (from Republican Dean Heller of Nevada), proponents and opponents were decamping to the other side of the Capitol, believing a climactic debate in the House during the coming months may be moving toward inevitability.

Advocates of the bill — which would outlaw workplace discrimination against gay, lesbian, bisexual and transgender people — are working to create something of a self-fulfilling prophecy: The metaphoric arc of history is bending so quickly toward this measure of justice that, by the time midterm Election Day arrives in one year, Republicans in close races will appear dangerously out of touch unless they have become part of turning ENDA into law.

Critics say they’re confident in their view of a very different political dynamic: Voters will remain much more worried about boosting the economy than about creating more costly, religious-freedom-impinging, and maybe even unnecessary, business regulations for the benefit of narrow and out-of-the-mainstream interests.

The House’s top two leaders have encapsulated those sentiments in recent days.

Speaker John A. Boehner “believes this legislation will increase frivolous litigation and cost American jobs,” his spokesman Michael Steele said Monday, reiterating the top Republican’s longstanding plans to keep the bill bottled up.

Minority Leader Nancy Pelosi said she believed she could pressure the GOP hierarchy into applying a lesson from the expansion of the Violence Against Women Act, which Boehner ushered through the House this winter without a majority of his majority, concluding that doing otherwise would worsen the GOP’s potentially debilitating gender gap.

“We made it too hot to handle in the public. It had to come to the floor,” the California Democrat said of her party’s tactics. “We would hope that once burned, twice learned.”

Women are a majority of the electorate, and Democrats won their 2012 vote by 9 points. The 5 percent who told the exit pollsters they were gay, lesbian or bisexual preferred the Democrats by 54 points. Those are just two of the numbers that have prompted so much strategic soul-searching about softening the party’s image on social issues.

Proponents of ENDA will be concentrating their efforts on rounding up House co-sponsors, hoping momentum from the growing roster of supporters in the Senate (on top of significantly expanded congressional support for gay marriage in the past year) can create an absolute majority of committed “yes” votes in the House.

All but a dozen Democrats have signed on, and perhaps half of the holdouts may yet do so. At least four look destined to vote “no” because they cited the GOP arguments in opposing the somewhat narrower version of ENDA the House passed in 2007. They are John Barrow of Georgia, Mike McIntyre of North Carolina and Nick J. Rahall II of West Virginia — all looking at tight races in swing districts in 2014 — plus Daniel Lipinski of Illinois.

That breadth of Democratic support would still require advocates to find about two dozen Republican votes, or about 10 percent of members. That’s a tall order in a GOP conference where many more members are more concerned about primary challenges from their right than about winning general elections in the center. And Boehner maintains he won’t call up the bill, even if it secures enough commitments to pass.

That situation is why one of the tactics under increased discussion would be replicating what happened in 2010 with the repeal of the “don’t ask, don’t tell” restrictions on gays in the military: Working to attach ENDA to a must-pass bill with considerable Republican support, such as the annual defense authorization measure, and gambling that enough conservatives would rather swallow the gay rights language than imperil the Pentagon budget.

Only five Republicans are co-sponsoring the stand-alone bill so far. And only one of those is in a competitive race where social policy liberalism looks to work to his benefit: Chris Gibson, who’s running for a third term in a Hudson Valley and Catskill Mountains district of New York. President Barack Obama carried that district by 6 points. Gibson is running against Democrat Sean Eldridge, who is married to Facebook co-founder Chris Hughes and has spent much of his career as an advocate for marriage equality.

The other four GOP backers are centrist Jon Runyan of central New Jersey, libertarian-tinged Richard Hanna of upstate New York and two of the veteran moderates who voted for the narrower bill six years ago: Ileana Ros-Lehtinen of Florida and Charlie Dent of Pennsylvania.

Ten other Republicans remain from that group, including Budget chairman and 2008 vice presidential nominee Paul D. Ryan of Wisconsin, National Republican Congressional Committee Chairman Greg Walden of Oregon, House Administration Chairwoman Candice S. Miller of Michigan, incoming Defense Appropriations Subcommittee Chairman Rodney Frelinghuysen of New Jersey, and Boehner confidant Pat Tiberi of Ohio.

All of them have signaled opposition to this year’s iteration because it would extend federal job bias protections to transgender people, whom the 2007 bill did not mention in a calculated effort by its sponsors to boost the GOP vote total. While 35 Republicans voted “yes,” only a handful of the 25 Democrats who voted “no” said they did so to protest the bill’s lack of inclusiveness.

Among those Democrats was Maine’s Michael H. Michaud, who revealed he is gay Monday in an op-ed published by two of the state’s biggest newspapers — a response, he said, to the “whisper campaigns, insinuations and push-polls” of his opponents in next year’s race for governor.

Dropping the transgender provision now doesn’t look to be on the table, for several reasons: A bill including that clause is going to get decent GOP support in the Senate. Taking the language out won’t unlock a surge of GOP support in the House, because most of those members still view the bill as an affront to family values and free enterprise.

What’s more, the gay rights community now looks united behind a strategy of waiting for the comprehensive victory it is confident will come before too long.