When those disclosures received what was seen as insufficient attention, the report said, the G.R.U. “relayed material it acquired from the D.N.C. and senior Democratic officials to WikiLeaks.” The founder of WikiLeaks, Julian Assange, has denied that Russia was the source of the emails it published.

The report makes clear that Mr. Putin favored Mr. Trump in part because he had previous success dealing with “Western political leaders whose business interests made them more disposed to deal with Russia” — it named a former Italian prime minister, Silvio Berlusconi, as an example — and in part because he viewed Mr. Trump as a more likely ally in forming Russia’s version of a counterterrorism coalition against the Islamic State. Mr. Trump described his eagerness to do so in an interview with The New York Times in March 2016.

The report also stated that Russia collected data “on some Republican-affiliated targets,” but did not disclose the contents of whatever it harvested.

The report’s introduction called the public document a summation of “a highly classified assessment.” The classified version, officials say, comes in two forms — one for Congress and another, called a “compartmentalized” report, for select members of Congress and top officials of the incoming and outgoing governments.

The compartmentalized version contains information on the sources and methods used to collect the information about Mr. Putin and his associates. Those would include intercepts of conversations and the harvesting of computer data from “implants” that the United States and its allies have put in Russian networks.

The conclusions were described to Mr. Obama on Thursday and to Mr. Trump on Friday by James R. Clapper Jr., the director of national intelligence; John O. Brennan, the director of the C.I.A.; Adm. Michael S. Rogers, the director of the National Security Agency; and James B. Comey, the director of the F.B.I.