US President Barack Obama's Republican foes elected their leader John Boehner speaker of the House of Representatives as a new US Congress convened Wednesday, ushering in a tense era of power-sharing.

In a vote made a mere formality by the robust Republican majority, Boehner beat Democratic Representative Nancy Pelosi by a 241-173 margin to become the third-ranking US elected official.

"We gather here today at a time of great challenges," he said in excerpts of his inaugural address, citing high unemployment, painful health care costs, and a swelling national debt now at 14 trillion dollars.

Republicans have vowed to slash spending, scrap "job-killing" government regulations, overhaul the tax code, crack down on undocumented immigration, cut diplomatic and foreign aid funds, and investigate the administration.

And they have already scheduled a January 12 vote on repealing Obama's signature overhaul of US health care -- a purely symbolic step because the Democratic Senate majority can block it and the president can veto it.

Boehner's election formally brought an end to Pelosi's tenure as Speaker four years after she was picked as the first woman to hold the post, which falls second in line for the presidency behind only the vice president.