* Analysts say Obama has year to meet legislative goals
* Speech to focus on the economy
* Obama to announce 34,000 troops to return from Afghanistan
* Supporters want details on climate change, gay rights
President Barack Obama will give his State of the Union address on Tuesday with an eye on the political calendar as time ticks down on his bid to advance an agenda that will help shape his White House legacy.
Just three months after winning re-election on Nov. 6, the Democratic president has a narrow window to push through policy priorities on the economy, immigration reform and gun control.
Analysts say he has roughly a year before Washington turns its attention to the 2014 mid-term elections, which could sweep more Republicans into Congress and accelerate the subsequent "lame duck" status that defines presidents who are not running for office again.
"He basically has a year for major legislative accomplishments because after the first year you get into the mid-term elections, which will partially be a referendum on his presidency," said Michele Swers, an associate professor of American government at Georgetown University.
Obama's speech at 9 p.m. EST on Tuesday (0200 GMT Wednesday) - an annual event in which the president lays out his policy priorities for the year - will be a chance for him to build momentum within that tight time frame.
"I don't want to say it's the last important speech he's going to give, but the window for a second-term president is fairly narrow," said Tony Fratto, a White House spokesman under former Republican President George W. Bush.
With unemployment still high and massive "sequester" spending cuts looming, administration officials say Obama will use the address before a television audience of millions to press Congress to support his proposals to boost the economy.
The White House is eager to show Obama's commitment to the economy is as great as it is to immigration and gun reforms, and he is expected to spend most of his speech reviving a theme that dominated his 2012 campaign: helping the middle class.
"You will hear ... an outline from him for his plan to create jobs and grow the middle class," White House spokesman Jay Carney said on Monday.
"His principal preoccupation as president has been the need to first reverse the devastating decline in our economy and then set it on a trajectory where it's growing in a way that helps the middle class, makes it more secure and makes it expand."
On foreign policy, Obama will outline steps to unwind U.S. involvement in the unpopular Afghanistan war and plans to announce that 34,000 U.S. troops will return by early 2014, a source familiar with the speech told Reuters.
The State of the Union also comes less than 24 hours after North Korea conducted a nuclear test that Obama in a statement called a "provocative act." A White House aide said the test will not force a change in Obama's speech.
"You'll hear the president address this, but he was always planning to deal with North Korea in his speech," senior adviser Dan Pfeiffer said on MSNBC.
The White House has signaled Obama will urge U.S. investment in infrastructure, manufacturing, clean energy and education, despite Republican opposition to increased government spending and a political divide over how to tame the budget deficit.
"He will demonstrate concretely how we have to invest in manufacturing, making the United States a magnet for job growth, preparing our work force, and making sure that if you work hard that you can earn a good living," senior adviser Valerie Jarrett said on NBC's "Today" show.
But the likelihood of passing new short-term economic initiatives that require government spending in the Republican-controlled House of Representatives is low.
Congressional Republicans said they would be listening for new ideas on how to control spending and avoid looming "sequester" budget cuts with an approach that does not rely heavily on additional tax increases.
House Speaker John Boehner said Obama did not have the "guts" to take on the liberal wing of his party and reach agreement with Republicans.
"To do the kind of lifting that needs to be done, I don't think he's got the guts to go do it," Boehner told a group of television anchors and reporters, according to CNN. "He doesn't have the courage to take on the liberal side of his own party."
U.S. Senate Democrats plan to unveil later this week a series of targeted spending cuts and tax increases on top earners to replace the sequester, but it is expected to be quickly rejected by Republican leaders.
"We're done with the tax part of the equation. If the president really wants a 'balanced' approach, now's the time to show his hand on the spending cuts and reforms he'll accept," Senate Republican leader Mitch McConnell said on the Senate floor on Tuesday.
Obama's speech is also expected to include a call for comprehensive trade talks with the 27-nation European Union.
Obama's advisers argue that his push for immigration reform is also an economic issue, and momentum for change is stronger there than it is for the president's other policy priorities.
U.S. Senator Marco Rubio - a Republican Cuban-American who is championing immigration reform albeit with a more restrictive process of legalization than Obama supports - will give his party's response to Obama's speech.
The debate over immigration will also play out in the balconies of the House of Representatives, where some members of the public will sit to listen to the speech. Representative Luis Gutierrez of Illinois plans to bring a man who is fighting deportation as his guest to the speech.
Prospects for success on gun control are in doubt, but the president is likely to use his speech to seek more support for proposals he laid out last month after the Newtown, Connecticut, school shooting massacre in which 20 schoolchildren died.
After giving prominent mention to the fight against climate change and equality for gays in his inaugural address, supporters will be disappointed if he fails to lay out details in those areas. Obama could advance both issues through executive orders, circumventing Congress and doing more to bolster his legacy.
"A second-term State of the Union is usually written with an eye on history books and I'm sure the president is thinking about what his legacy is going to be," said Doug Hattaway, a Democratic strategist and former adviser to Hillary Clinton.
Iran's nuclear ambitions and the festering civil war in Syria may present Obama with the toughest foreign policy tests of his second term, but they are likely to receive little attention in his speech.
He might raise concerns about cyber attacks, which have hit a succession of major U.S. companies and government agencies in recent months.
Obama will travel to three states in the days after his speech to sell his proposals to the public.