* Putin holds first nationwide phone-in of new presidency
* Addresses topics from pensions to Boston bombs
* Signals he will not dismiss his prime minister
By Timothy Heritage
MOSCOW, April 25 (Reuters) - President Vladimir Putin said on Thursday the Boston bombings proved his tough line against militants in the North Caucasus was right and showed Russia and the United States must step up cooperation on security.
After receiving almost 2 million questions from the Baltic Sea to Russia's far east, Putin used his annual "hotline" call-in to present the image of a man still in control a year into his third term and not afraid of criticism at home and abroad.
"If we truly join our efforts together, we will not allow these strikes and suffer such losses," he said of the bombings in the four-and-three-quarter-hour phone-in, which critics say now looks outdated as he fields predictable questions from loyal factory workers, airforce pilots and struggling mothers.
But this time he made sure there were critical voices in the audience, with a liberal journalist asking whether a clampdown on opponents since his return to the Kremlin last May echoed the repressions of Soviet dictator Josef Stalin.
Putin denied the accusation, but told the editor that Russia needed order and discipline. Former finance minister Alexei Kudrin also took him to task over the country's slide towards recession but Putin dismissed him jokingly as a "slacker".
There was even one written question seeking advice on how to handle a wayward son. This prompted a laugh but may have pleased Putin, who sees himself as the father of the nation and spoke of traditional and conservative values throughout the call-in.
Most of the time Putin looked stern as, sitting at a desk in a packed television studio, he took questions on issues ranging from pensions and roads to the ethnic Chechens suspected of carrying out the Boston Marathon bombings.
He avoided criticising the U.S. failure to prevent the bombings despite Russia's concerns about the brothers, passed on by the security services. But he took the chance to justify using heavy force against Islamist militants who oppose Russian rule in Chechnya and other parts of the restive North Caucasus.
"We have always said that action is needed and not declarations. Now two criminals have confirmed the correctness of our thesis," the former KGB spy said.
Putin, who first asserted his authority by crushing a Chechen independence bid in a war over a decade ago, has long said the United States underestimates the security threat posed by the militants and rejected international accusations that Moscow's use of force in the region has been heavy-handed.
Putin's remarks underlined his intention to use heightened concern over security to win closer cooperation with the United States in the run-up to the Sochi Winter Olympics next February.
The Olympics are a pet project for Putin and intended as a showcase of what Russia can achieve. A fatal attack on the Games would put those efforts in doubt.
Although he accused the United States at one point of being an imperialist power, he said differences in certain areas should not stand in the way of cooperation in others.
Putin, 60, was taking part in his first question-and-answer show with the Russian public since returning to the presidency last May after four years as prime minister.
The marathon show, broadcast nationwide, has been an almost annual event since 2001 - he did not do one last year.
Critics say the format has become outmoded and shows Russia has not moved with the times under Putin, who is accused by the opposition of being out of touch and allowing the country to stagnate economically and politically.
Dmitry Oreshkin, a political scientist who sympathises with the opposition, said the format had become "too familiar".
"The hotline has turned into Comedy Club," said one opposition leader, Ilya Yashin, referring to a Russian TV show that features stand-up comics.
But Putin, whose approval rating still hovers above 60 percent, spoke fluently and looked at ease as he reeled off figures and answered questions - all of which he appeared to expect - as he sat in a suit and tie.
One of his aims was clearly to show he has reasserted his grip on power, which was undermined just over a year ago during the biggest street protests since he first rose to power.
The protests have since dwindled and the opposition remains disjointed although critics accuse him of violating human rights with a clampdown on dissenters.
He denied accusations that he uses courts for political ends to persecute critics such as protest leader Alexei Navalny, currently on trial for theft, and the Pussy Riot punk group, two of whose members are in jail for performing an anti-Putin protest song in a Moscow cathedral.
Putin also used the call-in to play down suggestions that he disagrees with his government over economic policy and show he will not respond to calls to dismiss Dmitry Medvedev, the long-time ally whom he replaced as president last year.
There has been speculation for months in the media and among political analysts that Putin could make Medvedev a scapegoat if Russia's economy continues to slide towards recession.
But in response to a question, Putin said: "There is no division between the government and the president, or the presidential administration (on the economy) ... The people have only been in their jobs about a year."