By Gwladys Fouche

OSLO (Reuters) - Former NATO chief Jens Stoltenberg, who became Norway's new finance minister on Tuesday, said engaging with the Trump administration on trade was key to avoiding tariffs as Europe braces for a potential transatlantic trade war.

The appointment of the widely respected veteran politician and diplomat at a time of global trade tensions could give Norway's struggling Labour government a boost in opinion polls ahead of September's parliamentary elections.

"My main advice is that one must spend time engaging with (the Americans), travel to (Washington) and speak with the administration, like we did with NATO," Stoltenberg told reporters as he took up his post in the finance ministry.

"We are going to do everything we can to avoid tariffs being imposed on Norway."

Stoltenberg was prime minister of Norway in 2000-2001 and 2005-2013. He headed the Western military alliance for a decade, including during U.S. President Donald Trump's first term, stepping down last year.

At NATO, Stoltenberg was dubbed the "Trump-whisperer" for convincing Trump to stick with the alliance after the U.S. president complained during his first term that allies were spending too little on defence and threatened to pull out.

Non-EU Norway, a country of 5.5 million with an export-oriented economy, fears it could be vulnerable to a transatlantictrade war should Trump go ahead with his threat to impose tariffs on European Union goods. Norway's main exports are oil, gas and fish.

Norway's eurosceptic Centre Party quit the government on Thursday in a dispute over the adoption of European Union energy policies, leaving the centre-left Labour to rule alone.

Labour has been lagging in polls ahead of the September vote. Stoltenberg was widely popular among Norwegians during his time at NATO and afterwards and could boost Labour's prospects.

The 65-year-old is an economist by training and was finance minister in 1996-1997. He is widely seen as a pragmatist centrist.

In 2022, Stoltenberg was due to become Norway's central bank chief but did not take up the role after then-U.S. President Joe Biden asked him to continue as NATO chief.

During his first stint as PM, Stoltenberg set up the so-called spending rule, a self-imposed rule that says that Norwegian governments should not use more than 4% of the total value of the sovereign wealth fund for national budgets.

That rule has since then been reduced to 3% as the fund has grown in value.

(Reporting by Gwladys Fouche, editing by Terje Solsvik and Ros Russell)