MOSCOW » The day after he returned from the Winter Olympics in Sochi, President Vladimir Putin gathered the 12 members of his national security council for a crisis meeting to manage a political implosion in Ukraine that, by all accounts, had surprised Russia’s political and military elite and, above all, infuriated Putin himself.

One prominent member of the council, Valentina Matviyenko, chairwoman of the upper house of Parliament, emerged from the meeting declaring that it was impossible that Russia would invade Crimea, yet a couple of days later Russian troops were streaming into the peninsula.

When Putin made his first public remarks on the crisis only three days ago, he said Russia would not support Crimea’s efforts to secede. On Friday, the Kremlin allowed a mass pro-secession rally in Red Square while senior lawmakers loyal to Putin welcomed a delegation from Crimea and pledged support to make it a new province of the Russian Federation.

An examination of the seismic events that sparked the most threatening East-West confrontation since the Cold War, based on Putin’s public remarks and interviews with officials, diplomats and analysts here, suggests that the Kremlin’s strategy emerged haphazardly, even misleadingly, over a tense and momentous week, as an emotional Putin acted out of what the officials described as a deep sense of betrayal and grievance, especially toward the United States and Europe.

Some of those decisions, particularly the one to invade Crimea, then took on a life of their own, analysts said, unleashing a wave of nationalistic fervor for the peninsula’s reunification with Russia that the Kremlin has so far proved unwilling, or perhaps unable, to tamp down.

The decision to invade Crimea, the officials and analysts said, was made not by the national security council but in secret among a smaller and shrinking circle of Putin’s closest and most trusted aides. The group excluded senior officials from the Ministry of Foreign Affairs or the cadre of comparatively liberal advisers who might have foreseen the economic impact and potential consequences of U.S. and European sanctions.

"It seems the whole logic here is almost entirely the product of one particular mind," said Fyodor Lukyanov, a Russian analyst and editor of the quarterly journal Russia in Global Affairs.

Some of Russia’s plans were clearly years in the making, including one to sever Crimea from Ukraine through Moscow’s political support for sovereignty and even reunification. Nevertheless, Putin’s strategy in the past two weeks has appeared ad hoc, influenced by events not always in his control.

"We shouldn’t assume there was a grand plan," said Mark Galeotti, an expert on Russia’s security forces from New York University who is in Moscow and regularly meets with security officials. "They seem to be making things up as they go along."

Putin’s decisions since the crisis began reflect the instincts, political skills and emotions that have characterized his 14 years as Russia’s paramount leader, including a penchant for secrecy, loyalty and respect, for him and for Russia. They also suggest a deepening frustration with other world leaders that has left him impervious to threats of sanctions or international isolation, such that he shrugged off threats by members of the Group of 8 countries to boycott this year’s summit meeting in Sochi.

Because of Putin’s highly centralized authority, Russia’s policies and actions in moments of crisis can appear confused or hesitant until Putin himself decides on a course of action. That was the case in the days when violence erupted in Kiev, prompting a frantic effort by the Europeans to mediate a compromise. Putin, perhaps preoccupied with the Olympics, did not send a representative to those talks until the agreement was ready to be initialed.

Dmitry Trenin, director of the Moscow Carnegie Center, said Russia’s role in Ukraine’s upheaval was "very passive" until the moment President Viktor Yanukovych’s government collapsed. This was true, he said, despite the Kremlin’s wariness about any new Ukrainian trade agreement with the European Union and its pledge in December to provide a $15 billion package of assistance to shore up the country’s faltering finances. Jolted by the government’s collapse, Trenin said, the Kremlin "sprang into action almost immediately."

He and other officials and analysts said Putin’s visceral reaction stemmed from the collapse of the agreement on the night of Feb. 21. Putin, by his own account at a news conference Tuesday, warned Yanukovych not to withdraw the government’s security forces from the capital, Kiev, one of the key demands of the agreement being negotiated.

"’You will have anarchy,’" Putin said he told him. "’There will be chaos in the capital. Have pity on the people.’ But he did it anyway. And as soon as he did it, his office and that of the government were seized, and the chaos I warned him about erupted, and it continues to this day."

By then, however, Yanukovych had lost the support of his party, whose members joined others in Parliament in ordering the security services off the barricades they had maintained around government buildings in Kiev. Yanukovych, fearful because of reports of armed protesters heading to Kiev from western Ukraine, packed up documents from his presidential residence and fled early the next morning. That night Putin was still assuring President Barack Obama in a telephone call that he would work to resolve the crisis.

By the next day, however, Ukraine’s Parliament had stripped Yanukovych of his powers, voted to release opposition leader Yulia Tymoshenko from prison and scheduled presidential elections. Russia’s initial response was muted, but officials have since said Putin fumed that the Europeans who had mediated the agreement did nothing to enforce it. Putin and other officials began describing the new leaders as reactionaries and even fascists that Russia could not accept in power.

"It was probably not just thought of today," Alexei Chesnakov, a political strategist and former Kremlin aide, said of Putin’s move in Crimea, "but the trigger came when it was clear that the authorities in Ukraine were not able to return to the compromise of the 21st."

Two days later Putin attended the closing ceremonies of an Olympics he hoped would be a showcase of Russia’s revival as a modern, powerful nation. He then ordered the swift, furtive seizure of a region that has loomed large in Russia’s history since Catherine the Great’s conquest. The decision to order in Russian forces appears to have occurred late or Tuesday or Wednesday among a smaller circle of Putin’s advisers.

The group, the officials and analysts said, included Sergei B. Ivanov, Putin’s chief of staff; Nikolai Patrushev, secretary of the security council; and Alexander Bortnikov, director of the Federal Security Service. All are veterans of the KGB, specifically colleagues of Putin’s when he served in the organization in Leningrad, now St. Petersburg, during the 1970s and 1980s.

The exclusions of other advisers, the analysts and officials said, underscored his increasing conservatism since he returned to the presidency in 2012 and faced not only popular protests but also mounting criticism from the United States and Europe of the country’s record on political and human rights.

"He has bit by bit winnowed out the people who challenged his world view," Galeotti said.

Neither Putin nor any other official has acknowledged ordering an armed incursion in Crimea, although Putin in his news conference said he had bolstered security at the bases of the Black Sea Fleet, headquartered in Sevastopol.

The deployment of the Russian forces — which the Ukrainian government has said ranged from 6,000 to 15,000 troops — remains a covert operation, the officials and analysts said, to sidestep international law and the need for approval by the U.N. Security Council, something Putin and others have repeatedly insisted was necessary for any military operations against another country.

"It’s a traditional thing — to deny the obvious," said Andrei Soldatov, a journalist and the author, with Irina Borogan, of a book on Russia’s intelligence services called "The New Nobility."

As long ago as 2008, when NATO leaders met in Bucharest to consider whether to invite Ukraine to begin moving toward membership, Putin bluntly warned that such membership would unacceptable to Russia, presaging the strategy that appears to be unfolding now.

According to a diplomatic cable published by WikiLeaks, Putin even questioned the legality of the Soviet Union’s transfer of the region to the authority of what was then the Ukrainian Socialist Soviet Republic in 1954.

"If we add in the NATO question and other problems, the very existence of the state could find itself under threat," Putin said, according to the cable, written by Kurt Volker, the U.S. ambassador to NATO at the time.

The question now is how far Putin intends to go.

Sergei Markov, a political strategist who advises the Kremlin, said it was not yet clear.

"He is improvising," he explained.

Steven Lee Myers, New York Times

© 2014 The New York Times Company