A Republican-led campaign against researchers who study disinformation online has zeroed in on the most prominent American government agency dedicated to countering propaganda and other information operations from terrorists and hostile nations.

The agency, the State Department’s Global Engagement Center, is facing a torrent of accusations in court and in Congress that it has helped the social media giants — including Facebook, YouTube and X — to censor Americans in violation of the First Amendment.

The attorney general of Texas, Ken Paxton, and two conservative digital news outlets last week became the latest plaintiffs to sue the department and its top officials, including Secretary of State Antony J. Blinken. The lawsuit said the center’s work was “one of the most egregious government operations to censor the American press in the history of the nation.”

The center faces a more existential threat in Congress. House Republicans blocked a proposal this month to reauthorize the center, which began in 2011 to counter the propaganda of terrorist groups like Al Qaeda and the Islamic State. A small agency, with a regular staff of 125 people, many of them contractors, and a budget of $61 million, the center coordinates efforts across the government to track and expose propaganda and disinformation from Russia, China and other adversaries. With its mandate set to expire at the end of next year, the center is now operating under a shroud of uncertainty, even though its supporters say there is no evidence to back the charges against it.

If the Republicans hold firm, as a core bloc in the House appear determined to do, the center would disband amid two major regional wars and a wave of elections in 2024, including the U.S. presidential campaign.

James P. Rubin, the center’s coordinator since early this year, disputed the allegations that his organization censored Americans’ comments online. The center’s legal mandate, he said, was to “focus on how foreign adversaries, primarily China and Russia, use information operations and malign interference to manipulate world opinion.”