WASHINGTON — Senior Republicans conceded on Tuesday that the grueling fight with President 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 criticized 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 Senator John Thune, Republican of South Dakota and chairman of the Senate Commerce Committee. “This is an issue that needs to have bipartisan support.”