Accurate U.S. intelligence did not stop Putin, but it gave Biden big advantages.

The United States intelligence agencies unearthed Russia’s war plans. They accurately assessed President Vladimir V. Putin’s intentions and, through strategic public releases of information, complicated his efforts to create a pretext to send his armed forces into Ukraine. They got the timing of his invasion right almost to the hour.

The success of American intelligence in reading Mr. Putin and stripping away any element of surprise is one of the most striking developments of the crisis and has had substantial implications as the conflict has exploded into bloodshed.

It was not enough in the end to deter Mr. Putin from carrying out the broad assault that got underway early on Thursday.

But the depth and quality of the American intelligence strengthened President Biden’s hand in bringing the trans-Atlantic alliance into a unified front against Moscow. It provided time to prepare waves of sanctions and other steps to impose a cost on Russia, dispatch troops to bolster NATO allies and move Americans out of harm’s way.

And after high-profile intelligence failures in Afghanistan, Iraq and other global crises over the past several decades, the accuracy of the intelligence gave the C.I.A. and the broader array of U.S. intelligence agencies new credibility at home and abroad.

The result has been a remarkable four months of diplomacy, deterrence and American-led information warfare, including the last-ditch effort to disrupt Mr. Putin’s strategy by exposing it publicly. Unlike the withdrawal from Afghanistan last year, it was executed almost flawlessly. Even the Germans and other European nations highly dependent on Russian-supplied gas signed onto the playbook.

Now, with the invasion underway, administration officials are considering how to continue the information war with Russia, highlight potential war crimes and push back on Moscow’s propaganda about its intentions in Ukraine, according to people familiar with the discussions.

As the Biden administration released information about the Russian plans over the past few months, intelligence officials took pains to conceal how they had collected the material.

Still, it was clear that the intelligence agencies relied on all of their assets: a rebuilt source network in Russia, government and commercial satellites tracking the movement of Russian troops, an improved ability to intercept communications, and even open-source material culled from Russian social media.

Advances in cryptology and electronic-intercept technology over the last decade, helped by an ever-increasing reliance on computer networks and mobile communication around the world, have vastly increased the kinds of intelligence the United States and its allies seek. Even though Mr. Putin himself avoids using electronic devices, a modern army must communicate, and soldiers carry unsecured phones in their pockets, creating ample collection targets.

American officials leaked material showing the doubts that Russia’s frontline commanders had about Moscow’s war plans, a demonstration of how closely Moscow’s military was being watched. Assessments of what Mr. Putin would do proved correct, even when many other experts guessed wrong.

The United States found more innovative ways to use its intelligence as the crisis built. William J. Burns, the C.I.A. director, confronted the Russian government with its own war plans. Avril D. Haines, the director of national intelligence, shared secret intelligence with allied governments to build support for the American assessment. And the White House and State Department shared some declassified intelligence publicly to expose Mr. Putin’s plans for “false flag” operations and deny him the pretext he wanted to invade.

The intelligence disclosures may not be over now that the invasion has begun. The Biden administration has made clear it does not want to take on the job of publicly calling out Russian troop movements. But it may continue its information releases, as officials mull various options to hold Russia accountable for its actions in Ukraine, according to people familiar with the discussion.

“The intelligence, from not only American but British and other sources, has been spot on,” said Senator Mark Warner, the Virginia Democrat who is the chairman of the Senate Intelligence Committee. While the intelligence agencies have been “out of their comfort zone” in releasing information, the disclosures have had an effect, he said.

“What it’s done is not only thrown Putin’s plan’s slightly off, it’s also really helped solidify the NATO alliance,” Mr. Warner said.

The administration, he added, should continue disclosing what it knows about Russian actions as the war continues.

“We, America and the West, have not been great at hybrid warfare,” Mr. Warner said. “Russia-slash-the Soviets have been practicing those dark arts for the last 100 years. I think we need to continue with real information to counter the Russian disinformation.”

Those ongoing efforts could involve countering Russian propaganda that frames Moscow as the guardians and liberators of the Ukrainian people, not an occupying force. It could also involve work to expose potential war crimes and try to give the lie to Russian claims that their war aims are limited.

“It’s not something you want to do forever or as a permanent feature of policy or it loses its novelty, but in extraordinary, life-or-death situations, it is justified,” said John E. McLaughlin, a former acting C.I.A. director. “I always found in confronting Russians with our knowledge of what they were doing, that they would inevitably deny it but that it threw them off balance to know that we knew. And I think it has rattled Putin this time.”

Some of the information the United States shared with allies, beginning with a trip to NATO by Ms. Haines in November, was initially greeted skeptically, according to Western officials. Many Europeans still remember the bad intelligence around the Iraq war.

But as the information provided grew and the Russian war plan played out as Ms. Haines had predicted, European officials shifted their view. The intelligence-sharing campaign ultimately succeeded in uniting Europe and America on a series of tough sanctions.

The campaign has “been a distraction to him, it’s been somewhat annoying,” James Clapper, a former director of national intelligence, said on Wednesday. But, he added, “It remains to be seen what difference it has made on his decision-making.”

Republicans have said Mr. Biden should have adopted a more aggressive strategy in providing military supplies to Kyiv. They have also criticized him for not acting earlier to impose stiff sentences on Russia to change Mr. Putin’s course of action.

It will take time to know if more and better weapons could have made a difference for the Ukrainian army’s defense. But administration officials have said they have had to act judiciously not to escalate the situation and not allow Mr. Putin to use the delivery of American military supplies as an excuse to start the war.

More clearly, American sanctions against Mr. Putin go only so far. It is European sanctions against Russia and its billionaire class that really bite, and it took time, and intelligence, for Europe to come on board with a tougher package of sanctions.

While the United States clearly has the some of the best, if not the best, intelligence collection in the world, it also had a reputation that remained tarnished, at home and abroad, by the 2003 Iraq invasion, when faulty information was publicly released to justify the war. And while the intelligence community had long been pessimistic about the survival prospects for the U.S.-supported Afghan government, some in the administration criticized the spy agencies last year for not accurately predicting how quickly the country’s military forces would fold to the Taliban.

That reputation increased some of the skepticism of the assessment of Mr. Putin’s intentions, both by reporters questioning public officials for more evidence, and by allies.

The warnings this time were far different, the information released to try to prevent a war, not to start one. But releasing the information was nevertheless a risk. Had it proved wrong, the intelligence agencies would have been saddled with fresh doubts about their ability to collect and properly analyze intelligence about adversaries. That could have undermined efforts to credibly warn against future threats.

Instead, the public got a rare glimpse of an intelligence success. It is usually the failures, or partial failures — like Iraq, the Sept. 11, 2001, terror attacks or the Bay of Pigs — that are publicly aired.

But America’s spy agencies have in fact had many successes over the years, said Nicholas Dujmovic, a former C.I.A. historian who now teaches at the Catholic University of America.

“This is a rare case that intelligence successes are being made public, and the public should conclude, in my view, that this is rather the norm,” Dr. Dujmovic said. “They are getting a rare glimpse of the normal process and production of intelligence that normally they do not see.”

Most accusations of intelligence failures are failures to properly warn about an attack or to overstate a threat. And it is those warnings that this time proved prescient.

“The warning analysts have the hardest job in analysis because they are trying to figure out intentions — whether the attack will come, when it will come, how it will come,” Dr. Dujmovic said. “The best way to penetrate that fog is with a human source close to the decision maker, in this case, Putin — and it’s also the hardest kind of collection to acquire.”

The intelligence agencies succeeded in divining Mr. Putin’s intentions early on. And that was no easy feat. While the details and the strength of America’s source network in Russia are not publicly known, it is clear Mr. Putin shares his counsel with very few.

A televised meeting of Russia’s national security aides on Monday showed Mr. Putin berating his foreign intelligence chief for failing to endorse recognition of the breakaway enclaves in Eastern Ukraine. Juxtaposed with the months of American disclosures, the scene suggested that people atop America’s spy agencies, for once, may have understood Mr. Putin’s intentions better than his own intelligence officers.