After a weekend when Americans took to social media to debate President Trump’s admonishment of N.F.L. players who do not stand for the national anthem, a network of Twitter accounts suspected of links to Russia seized on both sides of the issue with hashtags such as #boycottnfl, #standforouranthem and #takeaknee.

As Twitter prepared to brief staff members of the Senate and House intelligence committees on Thursday for their investigation of Russian interference in the 2016 election, researchers from a public policy group have been following hundreds of accounts to track the continuing Russian operations to influence social media discourse and foment division in the United States.

For three weeks, a harsh spotlight has been trained on Facebook over its disclosure that Russians used fake pages and ads, designed to look like the work of American activists, to spread inflammatory messages during and since the presidential campaign.

But there is evidence that Twitter may have been used even more extensively than Facebook in the Russian influence campaign last year. In addition to Russia-linked Twitter accounts that posed as Americans, the platform was also used for large-scale automated messaging, using “bot” accounts to spread false stories and promote news articles about emails from Democratic operatives that had been obtained by Russian hackers.

Twitter has struggled for years to rein in the fake accounts overrunning its platform. Unlike Facebook, the service does not require its users to provide their real name (or at least a facsimile of one) and allows automated accounts — arguing that they are a useful tool for tasks such as customer service.

Beyond those restrictions, there is also an online black market for services that can allow for the creation of large numbers of Twitter bots, which can be controlled by a single person while still being difficult to distinguish from real accounts.

Since last month, researchers at the Alliance for Securing Democracy, a bipartisan initiative of the German Marshall Fund, a public policy research group in Washington, have been publicly tracking 600 Twitter accounts — human users and suspected bots alike — they have linked to Russian influence operations. Those were the accounts pushing the opposing messages on the N.F.L. and the national anthem.

Of 80 news stories promoted last week by those accounts, more than 25 percent “had a primary theme of anti-Americanism,” the researchers found. About 15 percent were critical of Hillary Clinton, falsely accusing her of funding left-wing antifa — short for anti-fascist — protesters, tying her to the lethal terrorist attack in Benghazi, Libya, in 2012 and discussing her daughter Chelsea’s use of Twitter. Eleven percent focused on wiretapping in the federal investigation into Paul Manafort, President Trump’s former campaign chairman, with most of them treated the news as a vindication for President Trump’s earlier wiretapping claims.

In the face of such public scrutiny, Twitter has said almost nothing about what it knows about Russia’s use of its platform. But Representative Adam Schiff of California, the top Democrat on the House Intelligence Committee, said he would like to know exactly what the company has done to find covert Russian activity and what it has discovered so far about fake accounts — including their reach and impact.

“I think right now the public is aware of only a subset of a subset of Russian activity online,” Mr. Schiff said in an interview. He said Facebook long denied that there had been Russian exploitation of its system, before reversing course on Sept. 6.

Mr. Schiff said the tech companies have asked for assistance from American intelligence agencies in trying to find and stop illicit interference from other countries, a request he said he supports.

The House Intelligence Committee announced on Wednesday that it would hold a public hearing on the matter of Russian influence next month, and a Senate aide said Facebook, Twitter and Google have been invited to testify at a Senate Intelligence Committee hearing on Nov. 1.

This month, The New York Times reported on evidence of Russian operators creating hundreds or thousands of fake Twitter accounts to flood the network with anti-Clinton messages during the campaign. The cybersecurity company FireEye identified what it called “warlists” of accounts linked to Russian intelligence that sometimes spewed messages like #WarAgainstDemocrats several times a minute.

Both DCLeaks and Guccifer 2.0, which spread the leaked emails and documents and were identified as having been created by Russian intelligence, used accounts that Twitter has not suspended, though they have been dormant for months. In some cases, the Russian exploitation of Facebook and Twitter was linked: “Heart of Texas,” a Facebook page advocating the secession of Texas that was identified as one of 470 fake profiles and pages linked to Russia, also had a Twitter feed — now suspended — called @itstimetosecede.

Experts on Russia inside and outside the government say President Vladimir V. Putin had multiple goals in last year’s campaign of hacking, leaking and stealth propaganda. He hoped to damage, if not defeat, Mrs. Clinton, whom he blamed for encouraging pro-democracy protests in Russia and neighboring states.

But Mr. Putin also sought to darken the image of the United States, making it a less attractive model for other countries and reducing its international influence, said Mark R. Jacobson, a Georgetown professor and co-author of a new report on Russian influence operations.

Last week, Facebook said it was turning over more than 3,000 Russia-linked ads to Congress. Many of those ads, like the opposing Twitter hashtags on the N.F.L. anthem issue, targeted divisions in American society by simultaneously sending conflicting messages to different users segmented by political and racial characteristics.

“What we see over and over again is that a lot of the messaging isn’t about politics, a specific politician, or political parties,” said Laura Rosenberger, director of the Alliance for Securing Democracy. “It’s about creating societal division, identifying divisive issues and fanning the flames.”

Her group’s web “dashboard” is called Hamilton 68. It is named for No. 68 of the Federalist Papers, believed to have been written by Alexander Hamilton, which warns of foreign meddling in American elections. The tool does not identify the activity of specific Twitter users but highlights the activity of the 600 accounts that researchers believe are either tied to the Russian government or repeat the themes of its propaganda.

For its part, Twitter has not said much about what it plans to say in the Congressional briefing.

“Twitter deeply respects the integrity of the election process, a cornerstone of all democracies, and will continue to strengthen our platform against bots and other forms of manipulation that violate our Terms of Service,” Twitter said in a statement.

Twitter has also said it was working to crack down on bots that distribute tweets en masse or that attempt to manipulate the platform’s trending topics.

Colin Crowell, Twitter’s vice president of public policy, government and philanthropy, said in a blog post in June that the company should not be an arbiter of whether a tweet is truthful or not.

Because Twitter is open and real-time, he said the platform is the best antidote to misinformation, when “journalists, experts and engaged citizens Tweet side-by-side correcting and challenging public discourse in seconds.”

Karen North, a social media professor at the University of Southern California’s Annenberg School for Communication and Journalism, said the company’s defense has some merit.

“Twitter functions more like a broadcast network,” she said. “People say things and everyone can hear it. When false information is stated, people can jump on false statements and challenge it.”