MOSCOW — Vladimir V. Putin took the oath of office on Monday for a fourth term as Russia’s president, in a ceremony staged in a gilded Kremlin hall once used to crown czars and replete with pageantry, highlighting his vast accumulation of authority after nearly two decades in power.

Mr. Putin, a former KGB agent, has ruled Russia as prime minister or president for more than 18 years, and in that time has crafted an image as a steely nerved leader and the man best qualified to rebuild his country after the collapse of the Soviet Union.

[Update: Putin endorses legislation enabling him to run for president again.]

In a theatrical touch, a televised ceremony began on Monday with Mr. Putin sitting at his desk in the Kremlin, suit jacket looped over his chair, as if hard at work until moments before the ceremony. A phone rang, letting him know it was time for his fourth term; he donned his jacket and walked alone through the red-carpeted Kremlin corridors and into a hall packed with about 6,000 invited, cheering guests.

In a short speech, Mr. Putin suggested his focus had now turned to domestic matters and improving Russia’s economy for the “well-being of every family,” though there were no words of reconciliation in the country’s tense relations with the West.