WASHINGTON -- U.S. President Barack Obama made a passionate pitch for gun control Tuesday in his fourth State of the Union address as the nation still reels from perhaps its most heinous mass shooting and the 20 first graders who were mowed down by a troubled young man with an assault weapon.

"In the two months since Newtown, more than 1,000 birthdays, graduations, and anniversaries have been stolen from our lives by a bullet from a gun," Obama said as he addressed a joint session of Congress, where tougher gun control laws have scant hope of passing despite overwhelming public support.

"This time is different," the president insisted.

Obama and congressional Democrats have been trying to push through gun control reforms that would mandate universal background checks and limit high-capacity ammunition magazines. One proposal, from California Sen. Dianne Feinstein, calls for a ban on assault weapons.

The president called on Congress to vote on all of the proposals. But many congressional Republicans, in particular -- and the powerful National Rifle Association that can make or break their political careers -- staunchly oppose such measures.

"Gabby Giffords deserves a vote," Obama said of the former Arizona congressman shot in the head by a would-be assassin in early 2011.

As he recited the names and locales of those involved in other mass shootings, Democratic lawmakers and the families of shooting victims tearfully applauded.

"The families of Newtown deserve a vote. The families of Aurora deserve a vote. The families of Oak Creek, and Tucson, and Blacksburg, and the countless other communities ripped open by gun violence -- they deserve a simple vote. They deserve a simple vote," he said.

Obama's plea for gun control, prompting thunderous applause and chants of "vote, vote, vote" from Democratic lawmakers, was the most powerful moment of a lengthy, substantive State of the Union address.

The speech focused primarily on his administration's efforts to ensure the current U.S. economic recovery is not a fleeting one.

"Together, we have cleared away the rubble of crisis, and can say with renewed confidence that the state of our union is stronger," Obama told lawmakers during the speech, replete with the pomp and circumstance that is characteristic of the annual event.

But he acknowledged that millions of Americans still cannot find work, adding that wages and incomes have "barely budged" despite soaring corporate profits.

"It is our generation's task, then, to reignite the true engine of America's economic growth -- a rising, thriving middle class."

The State of the Union was essentially a followup to the sweeping liberal agenda put forth by the president during his inaugural address three weeks ago. But this speech put Obama's proposals on the economy and job creation in sharper focus.

The president called for hiking the federal minimum wage as well as universal preschool for every four year old. He also urged US$1 billion in new manufacturing research, $50 billion in road repair funds and a new trade deal with the European Union

He insisted his proposals wouldn't add to the nation's staggering $16 trillion debt.

"Nothing I'm proposing tonight should increase our deficit by a single dime," he says. "It's not a bigger government we need, but a smarter government that sets priorities and invests in broad-based growth."

The president addressed Congress just as so-called sequestration -- a massive, mandated package of sweeping spending cuts to a host of federal agencies and departments -- is set to kick in on March 1. Some economists are warning sequestration could push the U.S. into another recession.

While the bulk of Obama's speech was about the economy and job creation, he also announced he's withdrawing more than half of the remaining American troops in Afghanistan in the months to come.

"Over the next year, another 34,000 American troops will come home from Afghanistan," he said. "This drawdown will continue. And by the end of next year, our war in Afghanistan will be over."

He added the nature of America's commitment in Afghanistan would change in the years to come.

"We are negotiating an agreement with the Afghan government that focuses on two missions: training and equipping Afghan forces so that the country does not again slip into chaos, and counter-terrorism efforts that allow us to pursue the remnants of al-Qaida and their affiliates," he said.

Canada withdrew its own combat troops in 2011, though an undisclosed number of Canadian soldiers are still in the country until 2014, helping to train and mentor the Afghan National Army. The Pentagon has told the White House it wants a small American military presence to remain as well.

The State of the Union is a president's annual chance to ask Congress to help him achieve his legislative agenda. But in 2013, lawmakers are bitterly divided on an array of fronts, including gun control, climate change, immigration reform and efforts to reduce the debt.

Those in the Canadian energy industry were watching closely on Tuesday night to see whether Obama would provide more details about the pledge he made to fight climate change during his second inaugural address on Jan. 21.

Obama reiterated that pledge on Tuesday.

"For the sake of our children and our future, we must do more to combat climate change," he said as legislators stood and applauded -- as they traditionally do dozens of times during the State of the Union.

"We can choose to believe that superstorm Sandy, and the most severe drought in decades, and the worst wildfires some states have ever seen were all just a freak coincidence. Or we can choose to believe in the overwhelming judgment of science -- and act before it's too late."

If Congress won't take action, the president added, he'll do it himself.

"We can make meaningful progress on this issue while driving strong economic growth. I urge this Congress to pursue a bipartisan, market-based solution to climate change .... But if Congress won't act soon to protect future generations, I will," he said.

The president vowed to direct his cabinet to come up with executive actions that can "reduce pollution, prepare our communities for the consequences of climate change, and speed the transition to more sustainable sources of energy."

He also proposed an Energy Security Trust that would foster new research and technology to shift cars and trucks off oil for good.

The natural gas boom has resulted in cleaner power and greater energy independence, Obama added, which in turn has prompted his administration to "keep cutting red tape and speeding up new oil and gas permits."

There was no mention specifically of TransCanada's Keystone XL pipeline. The U.S. State Department will make a decision on Keystone's latest permit application in the months to come because it crosses an international border.

There has been some speculation, however, that the president might soon announce plans to limit greenhouse gas emissions from existing power plants -- a decidedly "green" proposal that could cause consternation for proponents of Keystone XL, which would carry bitumen from Alberta's carbon-intensive oilsands to the Gulf Coast.

Environmentalists were also watching to see if the president made any mention of a carbon tax amid speculation that he might be plotting a carbon tax-Keystone XL tradeoff.

In that scenario, Obama holds off on making an ultimate decision on the pipeline until he gets bipartisan agreement on a revenue-raising carbon tax that would impose a levy on carbon entering the United States, including Canadian oil.

Bill McKibben, a leading U.S. environmentalist and Keystone opponent, had a lukewarm response to Obama's climate change remarks on Tuesday night.

"I'm glad to see the president, after the long, odd silence of the campaign, ratcheting up the rhetoric about climate change," he said in a statement. "The test of that rhetoric will be what he does about the purest, simplest test: the Keystone XL pipeline."

Obama was scheduled to go on the road immediately following his State of the Union, travelling to three states to appeal to Americans to back his efforts to improve the lot of the country's middle class and ensure it remains a land of opportunity for all.

After spending much of his first term mired in gridlock with congressional Republicans, Obama has reportedly decided the secret to success in his second term is getting the public behind his agenda.

In attendance for the State of the Union were the parents of shooting victim Hadiya Pendleton -- a Chicago teen killed last month by drug dealers a week after her majorette squad performed at the inauguration -- and Desiline Victor, a 102-year-old Haitian immigrant who waited in line for three hours to vote in Miami last fall.

They sat with first lady Michelle Obama.

The official Republican response to the speech was delivered by Florida Sen. Marco Rubio, who accused Obama of advocating "big government."

"Economic growth is the best way to help the middle class," Rubio said.

"That's why I hope the president will abandon his obsession with raising taxes and instead work with us to achieve real growth in our economy."