New NATO Secretary General Jens Stoltenberg arrives for his first day of work at NATO headquarters in Brussels on Wednesday, Oct. 1, 2014. A two-time prime minister, Stoltenberg became a recognizable face on the international scene with his dignified response to the twin terror attacks that killed 77 people in Norway in July 2011. (AP Photo/Virginia Mayo)(The Associated Press)

New NATO Secretary General Jens Stoltenberg arrives for his first day of work at NATO headquarters in Brussels on Wednesday, Oct. 1, 2014. A two-time prime minister, Stoltenberg became a recognizable face on the international scene with his dignified response to the twin terror attacks that killed 77 people in Norway in July 2011. (AP Photo/Virginia Mayo)(The Associated Press)

New NATO Secretary General Jens Stoltenberg, left, shakes hands with NATO Deputy Secretary General Alexander Vershbow as he arrives for his first day of work at NATO headquarters in Brussels on Wednesday, Oct. 1, 2014. A two-time prime minister, Stoltenberg became a recognizable face on the international scene with his dignified response to the twin terror attacks in Norway in July 2011. (AP Photo/Virginia Mayo)(The Associated Press)

New NATO Secretary General Jens Stoltenberg, left, walks with NATO Deputy Secretary General Alexander Vershbow as he arrives for his first day of work at NATO headquarters in Brussels on Wednesday, Oct. 1, 2014. A two-time prime minister, Stoltenberg became a recognizable face on the international scene with his dignified response to the twin terror attacks in Norway in July 2011. (AP Photo/Virginia Mayo)(The Associated Press)

BRUSSELS At a time of daunting geopolitical crises, NATO is undergoing its own version of regime change, with the arrival of a new chief official who has the blessing, at least temporarily, of one of the West's biggest adversaries: Russian President Vladimir Putin.

Former two-term Norwegian Prime Minister Jens Stoltenberg started work Wednesday as NATO's secretary-general, the 13th in the trans-Atlantic organization's 65-year existence. And the key question is whether his consensus-building style will be more effective in tamping down the Ukraine conflict and other flashpoints than the hard talk of his predecessor, Anders Fogh Rasmussen.

"I expect more moderate language, and that he will try to keep the dialogue open," said Kristian Berg Harpviken, director of the Peace Research Institute Oslo, an independent Norwegian research institution.

To allies like Germany, the expectation of a dial-back of the rhetoric from Rasmussen a former conservative Danish prime minister was one factor arguing in Stoltenberg's favor.

Last month, Foreign Minister Frank-Walter Steinmeier, though squarely blaming the Kremlin for the continued crisis over Ukraine, said: "I found that some things that came out of Brussels, from NATO headquarters, in these last few weeks weren't always helpful."

Stoltenberg was unanimously chosen as Rasmussen's successor by NATO's policy-making North Atlantic Council in March. It was a pick that won swift if tentative approval from Putin, who had dealt with Stoltenberg when the 55-year-old Norwegian headed the left-of-center government of one of Russia's neighboring countries.

Read more:

NATO gets a new chief_one Vladimir Putin has said he can do business with