President-elect Joe Biden is planning to move quickly to rebuild ties with longstanding U.S. allies and use those ties to coordinate international efforts to deal with Covid-19 and its economic and humanitarian consequences.

Early steps will include rejoining and trying to reform the World Health Organization while using international venues such as the Group of Seven nations and Group of 20 major economies to focus on the coronavirus pandemic and its consequences, including a potential debt crisis in emerging markets and food insecurity in impoverished nations, a top aide to Mr. Biden said.

As Mr. Biden campaigned for the presidency, he staked out sharply contrasting positions with President Trump on how to curb Iran’s nuclear program, pursue arms control with Russia and tackle climate change.

But the necessity of dealing with the pandemic is expected to dominate the start of the incoming administration’s foreign-policy efforts.

“There is an urgent leadership requirement internationally with regard to Covid-19,” said Antony Blinken, Mr. Biden’s senior foreign-policy adviser. “The first thing we have to deal with, domestically as well as internationally, is working to get out from under the Covid[-19] rock.”