WASHINGTON — The special counsel investigating Russian interference in the 2016 election issued an indictment of 12 Russian intelligence officers on Friday in the hacking of the Democratic National Committee and the Clinton presidential campaign. The indictment came only three days before President Trump was planning to meet with President Vladimir V. Putin of Russia in Helsinki, Finland.

The 29-page indictment is the most detailed accusation by the American government to date of the Russian government’s interference in the 2016 election, and it includes a litany of brazen Russian subterfuge operations meant to foment chaos in the months before Election Day.

From phishing attacks to gain access to Democratic operatives, to money laundering, to attempts to break into state elections boards, the indictment details a vigorous and complex effort by Russia’s top military intelligence service to sabotage the campaign of Mr. Trump’s Democratic rival, Hillary Clinton.

The timing of the indictment, by Robert S. Mueller III, the special counsel, added a jolt of tension to the already freighted atmosphere surrounding Mr. Trump’s meeting with Mr. Putin. It is all but certain to feed into the conspiratorial views held by the president and some of his allies that Mr. Mueller’s prosecutors are determined to undermine Mr. Trump’s designs for a rapprochement with Russia.

The president has long expressed doubt that Russia was behind the 2016 attacks, and the 11-count indictment illustrates even more the distance between his skepticism and the nearly unanimous views of the intelligence and law enforcement agencies he leads.

“Free and fair elections are hard fought and contentious, and there will always be adversaries who work to exacerbate domestic differences and try to confuse, divide and conquer us,” Rod J. Rosenstein, the deputy attorney general, said Friday during a news conference announcing the indictment.

“So long as we are united in our commitment to the shared values enshrined in the Constitution, they will not succeed,” he said.

It was a striking statement a day after Republican members of Congress, engaging in a shouting match during a hearing, attacked Peter Strzok, the F.B.I. agent who oversaw the early days of the Russia investigation, and questioned the integrity of the Justice Department for what they charged was bias against the president.

The announcement created a bizarre split screen on cable networks of the news conference at the Justice Department and the solemn pageant at Windsor Castle in England, where Mr. Trump and his wife, Melania, were reviewing royal guards with Queen Elizabeth II.

Russia has denied that its government had any role in hacking the presidential election, and on Friday, Mr. Trump said he would confront Mr. Putin directly. But the president said he did not expect his Russian counterpart to acknowledge it.

“I don’t think you’ll have any, ‘Gee, I did it, you got me,’” Mr. Trump said during a news conference hours before the indictment was announced. He added that there would not be any “Perry Mason” — a reference to the 1950s and 1960s courtroom TV drama in which Perry Mason, a criminal defense lawyer played by Raymond Burr, often got people to confess. “I will absolutely firmly ask the question.”

But Mr. Trump also said he believed that the focus on Russia’s election meddling and whether his campaign was involved were merely partisan issues that made it more difficult for him to establish closer ties with Mr. Putin.

The Kremlin agreed. A statement on Friday from Russia’s Foreign Ministry said that the indictment was meant to “spoil the atmosphere before the Russian-American summit.”

[Read the indictment here.]

After the indictment was announced, Senator Chuck Schumer of New York, the Democratic leader, and others in his party called on Mr. Trump to cancel his one-on-one meeting with Mr. Putin.

The indictment, Mr. Schumer said in a statement, was “further proof of what everyone but the president seems to understand: President Putin is an adversary who interfered in our elections to help President Trump win.” He added that “glad-handing with Vladimir Putin” would “be an insult to our democracy.”

The indictment builds on a declassified report released in January 2017 by several intelligence agencies, which concluded that “Putin and the Russian government aspired to help President-elect Trump’s election chances when possible by discrediting Secretary Clinton and publicly contrasting her unfavorably to him.”

Mr. Trump has long questioned the findings of intelligence agencies, suggesting alternate scenarios for who might have carried out the hacking campaigns. “It also could be somebody sitting on their bed that weighs 400 pounds, O.K.?” Mr. Trump said during the first presidential debate in September 2016.

Friday’s indictment did not include any accusations that the Russian efforts succeeded in influencing the election results, nor evidence that any of Mr. Trump’s advisers knowingly coordinated with the Russian campaign — a point immediately seized upon by the president’s allies.

Rudolph W. Giuliani, the president’s lawyer, said in a Twitter post that the indictment showed “no Americans are involved,” and he called on Mr. Mueller to end the inquiry. “The Russians are nailed,” Mr. Giuliani wrote.

Still, the indictment added curious new details to the events leading up to the November 2016 elections.

The indictment revealed that on July 27, 2016, Russian hackers tried for the first time to break into the servers of Mrs. Clinton’s personal offices. It was the same day that Mr. Trump publicly encouraged Russia to hack Mrs. Clinton’s emails.

“I will tell you this, Russia: If you’re listening, I hope you’re able to find the 30,000 emails that are missing,” Mr. Trump said during a news conference in Florida. “I think you will probably be rewarded mightily by our press.”

The indictment does not mention those remarks.

Separately, the indictment states that the hackers were communicating with “a person who was in regular contact with senior members of the presidential campaign.” Two government officials identified the person as Roger J. Stone Jr., a longtime adviser to Mr. Trump and the subject of close scrutiny by the F.B.I. and Mr. Mueller’s team. There is no indication that Mr. Stone knew he was communicating with Russians.

Communicating on Aug. 15 as Guccifer 2.0, an online persona, the Russian hackers wrote: “thank u for writing back … do u find anyt[h]ING interesting In the docs i posted?”

Two days later, the hackers wrote the person again, adding, “please tell me If i can help u anyhow … it would be a great pleasure to me.”

In another interaction several weeks later, the hackers, again writing as Guccifer 2.0, pointed to a document stolen from the Democratic Congressional Campaign Committee and posted online, asking, “what do u think of the info on the turnout model for the democrats entire presidential campaign.”

The person replied: “[p]retty standard.”

Friday’s indictment is a “big building block in the narrative being constructed for the American people regarding what happened during the election,” said Raj De, the chairman of the cybersecurity practice at Mayer Brown and the former general counsel of the National Security Agency.

By pulling together threads that Americans have read about for years — including the hacking of political institutions and campaigns, the dissemination of hacked emails and the attempts to compromise state election infrastructure — “this shows that the Russian campaign to impact the election was more coordinated and strategic than some have given it credit,” Mr. De said. “This indictment is our clearest window into that campaign.”

The document is a portrait of a coordinated and well-executed attack that targeted more than 300 people affiliated with the Clinton campaign, as well as other Democratic Party organizations. They implanted malicious computer code into computers, covertly monitored their users and stole their files that led to a series of disastrous leaks.

Investigators identified the 12 individuals in the indictment more than a year ago, according to a person with knowledge of the investigation who was not authorized to speak publicly about it.

Starting in April 2016, the hackers began to spread their stolen files using several online personas, including DC Leaks and Guccifer 2.0. The tens of thousands of stolen documents were released in stages that wreaked havoc on the Democratic Party throughout much of the election season.

The Russians also worked with people and organizations that were in a position to spread the information, including WikiLeaks, identified in the indictment as “Organization 1.”

According to the indictment, WikiLeaks wrote to Guccifer 2.0 in July 2016 asking for “anything Hillary related” in the coming days.

Most of the Russian intelligence officials charged in Friday’s indictment worked for the Russian military intelligence agency, formerly known as the G.R.U. and now called the Main Directorate.

While many of the broad elements of the Russian scheme were known before, investigators have not previously said how the Russian agents paid for the hacking campaign. The hackers’ use of cryptocurrency was one of the last pieces to fall into place for investigators in a case that they have been working on for more than a year.

The indictment released Friday said that the agents handled the most delicate transactions with the cryptocurrency Bitcoin. The Malaysian computer server that hosted DCLeaks.com, for instance, was paid for with the virtual currency.

Because Bitcoin functions without any central authority, the technology “allowed the conspirators to avoid direct relations with traditional financial institutions, allowing them to evade greater scrutiny of their identities and sources of funds,” the indictment said.

The Russian agents had several methods for acquiring Bitcoin, according to the indictment. At one point, the agents were actually mining new Bitcoin, a process that involves using computers to unlock new Bitcoin by solving complex computational problems.

The indictment’s extraordinary details may raise pointed questions about actions taken and not taken by American intelligence agencies and the Obama administration as the Russian campaign unfolded.

In many instances, the indictment describes the actions of individual Russian intelligence officers on particular dates. It is unclear from the indictment whether American intelligence agencies, primarily the National Security Agency, were watching in real time as the Russians prepared for and carried out their attacks against Democratic targets in spring 2016.

It was not until October 2016 that the government put out its first public statement on the Russian intrusion. If Americans knew much earlier about Russian actions, there will be questions about why they did not warn the targets, try countermeasures or call Russia out publicly before they did.

It is possible, however, that American spies did not detect the Russian attacks in real time, but reconstructed them later by studying the hacked Democratic networks and possibly breaking into Russian systems to examine logs.

Some experts said that the granular detail in the indictment was a warning to groups who might be eyeing future attacks.

“Even from a historical perspective, I can’t think of a case when someone went into this level of naming and shaming,” said Thomas Rid, a professor of strategic studies at Johns Hopkins University. “This is really significant.”

“There is going to be a deterrent effect on third parties,” he said. “If you are doing this kind of work, there are now so many examples of you finding your name in an indictment, it will definitely have an effect.”