U.S. President Barack Obama is announcing plans to scale back troops from Afghanistan and boost the U.S. economy as he delivers a closely watched State of the Union address laying out his priorities for the year ahead and for his newly begun second term in office.

The speech before a joint session of Congress' two chambers is expected to be dominated by domestic issues such as jobs, taxes and spending. But foreign policy priorities interjected in the hours before the speech, with North Korea announcing that it had detonated a nuclear device Tuesday. The White House said Obama would make the case that the nuclear program had only further isolated the impoverished nation.

The annual address is one of the biggest events in Washington. It is broadcast during prime evening viewing hours by the major television networks, with Washington's mightiest officials _ lawmakers, Supreme Court justices, military leaders and Cabinet members _ all in attendance and millions of Americans watching from home.

This year's speech comes at one of the strongest points in Obama's presidency. He won re-election by a convincing margin, is generally popular, and opposition Republicans appear weakened and fractured. Still, Republicans control the House of Representatives and tough fights loom on the budget and other top issues.

In his speech, Obama was pressing a theme central to his campaign: that government needs to ensure that every American, regardless of background, has an opportunity to succeed. He called it ``the basic bargain that built this country.''

``It is our unfinished task to make sure that this government works on behalf of the many and not just the few,'' he said, in excerpts released in advance of the speech.

With the economy still the biggest concern of most Americans, Obama was devoting less time to foreign policy this year.  But his announcement on the withdrawal of 34,000 troops from Afghanistan _ about half the force there _ is a major development, even if it was highly anticipated. It puts the United States on pace to formally finish the protracted war by the end of 2014.

Also, the timing of North Korea's nuclear test, just hours before the speech, was seen as a direct challenge to Obama. The president was expected to sharply rebuke North Korea, which appears to be making progress toward developing nuclear devices and missiles that could one day threaten the United States.

Obama was also using the address to press for congressional action on climate change and for stricter gun control laws, both of which face resistance from House Republicans. His push for overhauling immigration laws could get a warmer reception. It is one of the few major issues in which badly divided Republicans and Democrats can find common ground. Republicans have long opposed relaxing immigration laws, but are reconsidering their positions as they try to appeal to Hispanics, a growing part of the U.S. electorate that has overwhelmingly favored Democrats.

One of the leading Republican voices for immigration reform, Sen. Marco Rubio, will deliver the official Republican response. Rubio, a 41-year-old Cuban-American, is one of the party's brightest stars and a possible 2016 presidential candidate. But in a sign of the divisions in the party, another, unofficial Republican response will be given by Rand Paul, a senator who is a favorite of the small-government tea party movement.

Republicans remain united in their opposition to Obama's proposals for more spending at a time of huge deficits. Obama said his proposals to increase spending on manufacturing, infrastructure and clean-energy technologies would be fully paid for, though he did not specify in the excerpts how he would offset the cost of his proposals.

``Nothing I'm proposing tonight should increase our deficit by a single dime,'' Obama said.

He is also calling on Congress to prevent another potential blow to the economy on March 1, when massive, automatic spending cuts are scheduled to take place. Obama has asked lawmakers to block those cuts by approving a mix of tax increases and targeted budget cuts. Republicans oppose any further tax increases beyond those they reluctantly agreed to at the start of the year in exchange for extending tax cuts in effect since George W. Bush's presidency.

``He's gotten all the revenue he's going to get,'' said the Senate's top Republican, Mitch McConnell.

While Obama makes his case for greater gun control, first lady Michelle Obama will sit with the parents of a Chicago teenager shot and killed just days after she performed at the president's inauguration last month. Twenty-two House members have invited people affected by gun violence, according to Jim Langevin, a Democratic congressman who helped with the effort. And Republican congressman Steve Stockman says he's invited rocker Ted Nugent, a long-time gun control opponent who last year said he would end up ``dead or in jail'' if Obama won re-election.

Immediately following his speech, Obama will hold a conference call with supporters to urge them to pressure lawmakers to back his agenda. He'll also seek to rally public support with trips this week to North Carolina, Georgia and Illinois. (AP)