"I am absolutely confident President-elect Trump will maintain America's strong commitment to European security and to NATO," Stoltenberg told AFP in an interview in Brussels.
"That is in the interests of both Europe and the United States," he said, with the disasters of two World Wars and the Cold War showing how inter-connected both sides' security was.
The only time NATO's Article 5 "all for one, one for all," collective defence guarantee had been invoked was after the 9/11 terror attacks on the United States, he recalled.
Washington accounts for nearly 70 percent of the NATO allies combined defence outlays and has long demanded they do more.
Trump caused consternation on the campaign trail when he suggested Washington might think twice about coming to the defence of an ally if it had not paid its NATO dues.
NATO announced later today that Stoltenberg had had a "good talk" with Trump on the alliance's future.
He had thanked him in particular for raising the issue of defence spending, a "top priority" for the secretary general since he took office in 2014, it said in a statement.
Trump's more positive approach to President Vladimir Putin also rattled allies who at a July Warsaw summit had endorsed NATO's biggest military build-up since the end of the Cold War to counter a more assertive Russia.
Stoltenberg said he did not see an issue.
"What I have heard is that he has conveyed a message about also talking to the Russians. At our Warsaw summit, we made decisions on strong defence but also on political dialogue" with Moscow, he said.
Pundits in Europe largely took Trump's campaign comments at face value, wondering if the new president was about to ditch Washington's 70-year security guarantee for Europe in favour of a more isolationist, "America First," policy.
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