President Barack Obama takes center stage on Tuesday to try to sell the American people on his broader agenda for jolting the United States out of deep recession and confronting long-term economic challenges.

Riding high in opinion polls, Obama will deliver a State of the Union-style address at 9 p.m. EST in his first appearance before a joint session of Congress since he took office five weeks ago.

The primetime speech, the opening act on Capitol Hill for any new president, comes in a pivotal week for Obama. He will roll out his first budget proposal on Thursday against a backdrop of growing public anxiety over the worst economic crisis in decades.

In a stark reminder of how grim the situation has become, Wall Street slumped to a 12-year low on Monday as investors worried about the government nationalizing ailing major banks, a prospect the White House tried to play down.

Obama will be looking to trade on his popularity and personal suasion when he stands before the Senate and House of Representatives to try to reassure Americans about what he is doing -- and what he plans to do -- to halt the crisis.

The speech is sure to be his most closely watched performance since his January 20 inauguration as America's 44th president.

It won't be enough just to look presidential, said Stephen Wayne, a political scientist at Georgetown University. What he needs to be is explainer-in-chief.

STILL ON HONEYMOON

Seeking to build momentum, the Democratic president hosted a bipartisan summit on fiscal responsibility on Monday, pledging to halve the $1 trillion-plus federal deficit he inherited by the end of his term in 2013.

He is expected to hammer home that theme on Tuesday while also laying out a list of domestic priorities, ranging from overhauling healthcare to bolstering support for alternative energy -- promises he made during the presidential campaign.

While the economy will dominate Obama's speech, he is also likely to touch on foreign affairs as he keeps up efforts to roll back Republican President George W. Bush's most divisive policies and repair America's image abroad.

He is expected to stress the shift in U.S. military focus from Iraq to Afghanistan, underscored by a troop buildup he has ordered to help counter a Taliban resurgence.

Obama could also reassert his offer of direct diplomacy with U.S. foe Iran, a reversal of Bush's policy of isolating Tehran over its nuclear ambitions.

The speech comes at a time when Obama's presidential honeymoon is still going strong, despite Cabinet missteps that have strained his no-drama Obama image and criticism about a lack of specifics in some of his early financial initiatives.

The latest New York Times/CBS News poll gave him a job approval rating of 63 percent, about 10 points higher than either Bush or Bill Clinton at this stage. A new Washington Post-ABC News poll had 68 percent of Americans approving of Obama's job performance.

There was also strong support for the $787 billion economic stimulus package he pushed through the Democratic-controlled Congress this month despite heavy Republican opposition.

With the speech to Congress providing Obama with his most direct channel to the American people since his inaugural address, he will also take care to set the right tone.

Since taking office, he has largely ditched his campaign talk of yes, we can for a more sober message of bleak economic times and an outlook for even worse to come.

Reflecting misgivings among some Democrats about Obama's gloomy language, Clinton urged him last week to show more of the hope he promised as a candidate. Obama has insisted he is just painting a realistic picture.

(Editing by John O'Callaghan)

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