(Reuters) - President Barack Obama will join the battle over the U.S. "fiscal cliff" on Friday for the first time since voters gave him a second term in office, setting the stage for a showdown with congressional Republicans over sharp tax hikes and spending cuts slated to take effect early next year.

Obama is to make a statement from the East Room of the White House at 1:05 p.m. EST. His opening move in what is expected to be a tense negotiation to avert the so-called "fiscal cliff" was telegraphed Thursday by a top adviser, David Plouffe, who claimed a mandate from Tuesday's election victory to raise taxes on the wealthy.

That set up a clash with the Republican-controlled House of Representatives, whose leader, Speaker John Boehner, reiterated on Thursday his opposition to any increase in tax rates.

Boehner has scheduled his own news conference for Friday morning ahead of the president's statement.

The "fiscal cliff" of steep government spending cuts and tax rises due to be implemented under existing law in early 2013 may cut the federal budget deficit, but economists warn it also could tip the economy back into recession.

While disagreeing on immediate measures to avert the looming fiscal crisis, Obama and Republicans may find common ground in calls for enactment over the next six months of a larger package of deficit reduction measures, including a rewrite of U.S. tax laws.

The president called for negotiations on such a "grand bargain" during his campaign.

Obama, who defeated Republican challenger Mitt Romney in a race in which the two candidates offered different visions for spurring the sluggisheconomy, is not expected to put forward a new or specific plan.

Instead, he is more likely to urge Congress to tackle the fiscal cliff during its post-election session that begins next week.