American intelligence agencies sharply disagree, and their darker view of Russia’s actions was clear on Tuesday. Mr. Coats was joined at the hearing by the leaders of the Central Intelligence Agency, the National Security Agency, the F.B.I. and other intelligence agencies.
Russian hackers are already scanning American electoral systems, intelligence officials have said, and using bot armies to promote partisan causes on social media. Russia also appears eager to spread information — real and fake — that deepens political divisions, including purported evidence that ties Mr. Trump to Russia, and its efforts to influence the 2016 election.
“We expect Russia to continue using propaganda, social media, false-flag personas, sympathetic spokespeople, and other means of influence to try to exacerbate social and political fissures in the United States,” Mr. Coats said.
“We have seen Russian activities and intentions to have an impact on the next election cycle,” added Mike Pompeo, the director of the C.I.A.
The C.I.A. stood ready to identify elements of Russia’s information campaign and work with domestic law enforcement to respond, he said, suggesting it could go on the attack if needed.
“We do have some capabilities offensively to raise the cost for those who would dare challenge the United States elections,” Mr. Pompeo said.
Mr. Pompeo was also asked about reports last week by The New York Times and The Intercept that American intelligence agencies spent months negotiating with a Russian who said he could sell stolen American cyberweapons and insisted the deal would including purportedly compromising material on Mr. Trump. The negotiations were conducted through an American businessman who lives in Europe and served as a cutout for American intelligence.
Mr. Pompeo called the reporting “atrocious, ridiculous and inaccurate” and said the C.I.A. had not paid the Russian. The Times, citing American and European intelligence officials, said only that American spies had paid the Russian $100,000 for the cyberweapons using an indirect channel. The cyberweapons were never delivered. The Russian did provide information on Mr. Trump, which intelligence agencies refused to accept and remains with the American businessman.
Mr. Pompeo did appear to acknowledge the operation itself, saying that “the information we were working to try and retrieve was information we believed might well have been stolen from the U.S. government.”
Russia was far from the only topic covered at the hearing. Mr. Trump’s attacks on the F.B.I. as an agency infected by partisan bias were raised by senators and swatted away by Christopher A. Wray, the bureau’s director, who was appointed last year by Mr. Trump.
Asked directly whether he had seen any evidence of political bias at the bureau, he did not hesitate or equivocate: “No,” Mr. Wray said.
He offered a full-throated defense of the F.B.I., calling its employees “the finest group of professionals and public servants I could hope to work with.”
“I am a big believer in the idea that the F.B.I. speaks through its work, through its cases, through the victims it protects,” Mr. Wray said. “And I encourage our folks not to get hung up with what I consider the noise on TV and social media.”
The testimony on Tuesday also covered the slew of other threats that American intelligence agencies see facing the United States, including North Korea’s nuclear program, Islamist militants in the Middle East and even illicit drug trafficking, especially the smuggling of cheaply made fentanyl, a powerful opioid responsible for thousands of deaths each year.
But as has been the case for years, the intelligence leaders presented cyberactivities of rival nations and rogue groups as the foremost threat facing the United States. They warned that such risks were likely to only grow, citing Russia, China, Iran and North Korea, along with militant groups and criminal networks, as the main agitators.
A number of senators expressed concerns that China was seeking to use private companies with ties to its government to obtain sensitive American technology.
The efforts of Chinese companies to carve out a larger presence in the United States and sell more phones and other devices to ordinary Americans, represents “counterintelligence and information security risks that come prepackaged with the goods and services,” said Senator Richard Burr of North Carolina, the Republican chairman of the committee.
He singled out two Chinese companies, Huawei Technologies Co Ltd. and ZTE Corp, as examples of what he considered a troubling trend. Both are “widely understood to have extraordinary ties to the Chinese government,” Mr. Burr said.
The companies have repeatedly denied that the Chinese government is using them to spy on the United States.
Two Republicans on the committee, Senators Marco Rubio of Florida and Tom Cotton of Arkansas, introduced legislation last week to ban the United States government from buying or leasing telecommunications equipment from Huawei and ZTE. They said there were concerns the Chinese companies would use their access to spy on American officials, and American intelligence chiefs appeared to agree on Tuesday.
Mr. Cotton asked the assembled intelligence chiefs to raise their hands if they would use and phones or other devices from Huawei and ZTE, or recommend that ordinary Americans do so.
No hands went up.
“We’re deeply concerned about the risk of allowing any company or entity that is beholden to foreign governments that don’t share our values to gain positions of power inside our telecommunications networks,” said Mr. Wray.
Mr. Burr closed the hearing with an update on the committee’s own Russia investigation, promising to deliver a report and an open hearing on election security before this spring’s primaries ahead of the November midterm elections. The committee, he said, still hopes to also give conclusive answers on how the Russian campaign was carried out and whether any American individual, campaign or company coordinated with the Russians.