WASHINGTON >>  Senior Republicans conceded on Tuesday that the grueling fight with President Barack Obama over the regulation of Internet service appears over, with the president and an army of Internet activists victorious.

The Federal Communications Commission is expected on Thursday to approve regulating Internet service like a public utility, prohibiting companies from paying for faster lanes on the Internet. While the two Democratic commissioners are negotiating over technical details, they are widely expected to side with the Democratic chairman, Tom Wheeler, against the two Republican commissioners.

And Republicans on Capitol Hill, who once blasted the plan as “Obamacare for the Internet,” now say they are unlikely to pass a legislative response that would undo perhaps the biggest policy shift since the Internet became a reality.

“We’re not going to get a signed bill that doesn’t have Democrats’ support,” said Sen. John Thune, R-S.D., chairman of the Senate Commerce Committee. “This is an issue that needs to have bipartisan support.”

The new FCC rules are still likely to be tied up in a protracted court fight with the cable companies and Internet service providers that oppose it, and it could be overturned in the future by a Republican-leaning commission. But for now, Congress’ hands appear to be tied.

The FCC plan would let the agency regulate Internet access as if it is a public good. It would follow the concept known as net neutrality or an open Internet, banning so-called paid prioritization — or fast lanes — for willing Internet content providers.

In addition, it would ban the intentional slowing of the Internet for companies that refuse to pay broadband providers. The plan would also give the FCC the power to step in if unforeseen impediments are thrown up by the handful of giant companies that run many of the country’s broadband and wireless networks.

Republicans hoped to pre-empt the FCC vote with legislation, but Senate Democrats insisted on waiting until after Thursday’s FCC vote before even beginning to talk about legislation about an open Internet. Even Thune, the architect of draft legislation to override the FCC, said Democrats had stalled what momentum he could muster.

And an avalanche of support for Wheeler’s plan — driven by Internet companies as varied as Netflix, Twitter, Mozilla and Etsy — has swamped Washington.

“We’ve been outspent, outlobbied, we were going up against the second-biggest corporate lobby in D.C., and it looks like we’ve won,” said Dave Steer, director of advocacy for the Mozilla Foundation, the nonprofit technology foundation that runs Firefox, a popular Web browser, referring to the cable companies. “A year ago today, we did not think we would be in this spot.”

The net neutrality movement pitted new media against old and may well have revolutionized notions of corporate social responsibility and activism. Top-down decisions by executives investing in or divesting themselves of resources, paying lobbyists and buying advertisements were upended by the mobilization of Internet customers and users.

“We don’t have an army of lobbyists to deploy. We don’t have financial resources to throw around,” said Liba Rubenstein, director of social impact and public policy at the social media company Tumblr, which is owned by Yahoo, the large Internet company, but operated independently on the issue. “What we do have is access to an incredibly engaged, incredibly passionate user base, and we can give folks the tools to respond.”

Internet service providers say heavy-handed regulation of the Internet will diminish their profitability and crush investment to expand and speed up Internet access. It could even open the Web to taxation to pay for new regulators.

Brian Dietz, a spokesman for the National Cable & Telecommunications Association, said the pro-net-neutrality advocates turned a complex and technical debate over how best to keep the Internet operating most efficiently into a matter of religion. The forces for stronger regulation, he said, became viewed as for the Internet. Those opposed to the regulation were viewed as against the Internet.

The Internet companies, he said, sometimes mislead their customers and, in some cases, are misled on the intricacies of the policy.

“Many of the things they have said just belie reality and common sense,” he said.

In April, a dozen New York-based Internet companies gathered at Tumblr’s headquarters in Manhattan to hear dire warnings that broadband providers were about to obtain the right to charge for the fastest speeds on the Web.

The implication: If they did not pony up, they would be stuck in the slow lane.

What followed was the longest, most sustained campaign of Internet activism in history. A swarm of small players, like Tumblr, Etsy, BoingBoing and Reddit, overwhelmed the giants of the broadband world, Comcast, Verizon Communications and Time Warner Cable. Two of the biggest players on the Internet, Amazon and Google, largely stayed in the background, while smaller participants — some household names like Twitter and Netflix, others far more obscure, like Chess.com and Urban Dictionary — mobilized a grass-roots crusade.