WASHINGTON — President Trump said on Thursday that only “three or four” of the United States’ 17 intelligence agencies had concluded that Russia interfered in the presidential election — a statement that while technically accurate, is misleading and suggests widespread dissent among American intelligence agencies when none has emerged.

The “three or four” agencies referred to by Mr. Trump are the Central Intelligence Agency, the National Security Agency, the F.B.I. and the Office of the Director of National Intelligence, all of which determined that Russia interfered in the election. Their work was compiled into a report, and a declassified version was released on Jan. 6 by the director of national intelligence. It said that all four agencies had “high confidence” that Russian spies had tried to interfere in the election on the orders of President Vladimir V. Putin.

The reason the views of only those four intelligence agencies, not all 17, were included in the assessment is simple: They were the ones tracking and analyzing the Russian campaign. The rest were doing other work.

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The intelligence community is a sprawling enterprise that includes military officers who track enemy troop movements, accountants who analyze the finances of Islamist militants and engineers who design spy satellites. There are soldiers, sailors and Marines; tens of thousands of civilian government employees and tens of thousands of private contractors.

Asked about Russia’s election meddling during a news conference on Thursday in Poland, Mr. Trump repeated his familiar refrain that “it could” have been Russia or other countries that interfered in the election, and then appeared to suggest that there was hardly an intelligence community consensus on the matter.

“Let me just start off by saying I heard it was 17 agencies,” he said when asked about the intelligence assessment.

“I said, ‘Boy, that’s a lot.’ Do we even have that many intelligence agencies, right? Let’s check it. And we did some very heavy research,” Mr. Trump continued. “It turned out to be three or four — it wasn’t 17 — and many of your compatriots had to change their reporting, and they had to apologize, and they had to correct.”

Mr. Trump was also correct about inaccurate news reports. Some, including an article in The New York Times, incorrectly reported that all 17 American intelligence agencies had endorsed the assessment.

But there is no evidence that significant uncertainty or dissent exists across the intelligence community, simply because not all 17 were involved in the assessment of Russian interference.

Here is what you need to know about American intelligence agencies and what they do:

The Best-Known Agencies

When you think of a spy slipping into a darkened safe house to meet an informant, or furtively taking out an Islamist militant leader, you are thinking of someone who works for the C.I.A. It is the best-known American intelligence agency, and it conducts most of the country’s human intelligence and runs most covert operations. It also includes thousands of analysts whose job is to decipher foreign events for American leaders.

The N.S.A., where Edward J. Snowden worked, eavesdrops on calls and emails. Its bailiwick is what is known as signals intelligence — known among spies simply as “sigint” — and other forms of electronic spying, such as creating computer viruses that caused Iranian nuclear centrifuges to spin out of control or some North Korean missiles to veer off course.

The F.B.I. enforces federal law, as any good mobster knows. But it also has a role in the intelligence world, leading counterintelligence operations, which are efforts to understand and stop foreign espionage. (That is the work done by Stan Beeman, the fictional F.B.I. agent on “The Americans.”)

The Office of the Director of National Intelligence was created after the Sept. 11 attacks to coordinate the efforts of all the parts of the intelligence community. The idea was to ensure that the agencies were working together to avoid future attacks.

Smaller Parts of Big Agencies

A number of widely known government agencies have their own intelligence arms. The Bureau of Intelligence and Research at the State Department, for instance, helps American diplomats understand the world.

The Department of Energy’s Office of Intelligence and Counterintelligence helps protect sensitive laboratories and nuclear facilities. At the Department of Homeland Security, the Office of Intelligence and Analysis looks out for threats to the United States.

The Office of National Security Intelligence at the D.E.A. brings together intelligence from around the government to help stop drug smuggling. The Treasury Department has the Office of Intelligence and Analysis to help cut the flow of money to terrorist groups, drug lords and other criminals who operate internationally.

Then, of course, there is the Pentagon. Its main intelligence arm is the Defense Intelligence Agency, which is the third-largest intelligence agency. The Army, Navy, Air Force, Marines and Coast Guard also all have their own intelligence branches.

The Little-Known Agencies

The National Geospatial-Intelligence Agency decides what do with the images captured by American spy satellites. And the National Reconnaissance Office designs, builds and operates the satellites.

The work can be tricky. In 1999, a predecessor to the National Geospatial-Intelligence Agency incorrectly marked the Chinese embassy on maps of Belgrade, Serbia, which was inadvertently bombed by American warplanes, killing three and wounding 20. And in 2013, the agency incorrectly misplaced a reef by eight miles, leading to the grounding of the Guardian, a naval minesweeper.