CHARLOTTE, N.C. -- With his presidency on the line, President Obama on Thursday asked for more time from voters, acknowledging that despite his lofty goals of hope and change, the economy is going to take years to recover.

As he sought to regain trust from a disaffected electorate weary of months of high unemployment, Obama warned of tough times as the nation emerges from what he said are "challenges that have built up over decades." But he offered a rousing defense of his stewardship and insisted his vision -- not that of his Republican rival, Mitt Romney -- will lead to true prosperity for the middle class.

"Know this, America: Our problems can be solved. Our challenges can be met," Obama said. "The path we offer may be harder, but it leads to a better place. And I'm asking you to choose that future."

In a speech that at times seemed far from the soaring rhetoric of his first nomination speech, Obama asked the crowd to "rally around a set of goals for your country."

After attacking Romney for failing to offer specific proposals at the Republican National Convention in Tampa, Fla., last week, Obama outlined a series of goals including creating 1 million new manufacturing jobs, recruiting 100,000 math and science teachers and reducing the deficit by more than $4 trillion.

"They want your vote, but they don't want you to know their plan," Obama said. "And that's because all they have to offer is the same prescription they've had for the last 30 years."

Republicans immediately called the goals scaled down or recycled promises from 2008.

With polls showing the race even, Obama needed to enthuse a dispirited base and persuade the last few undecided voters that his prescription for prosperity will restore the middle class.

Obama cast the election as a choice between "two different paths for America," warning that "over the next few years, big decisions will be made in Washington, on jobs and the economy; taxes and deficits; energy and education; war and peace."

Obama blamed Republicans for preventing him from accomplishing more, but he did not fully explain how he would work with House Republicans in the future. He took some swipes at Romney, particularly on foreign policy, but he only once mentioned him by name, when he spoke about his disdain for providing tax breaks to the wealthy.

"No party has a monopoly on wisdom. No democracy works without compromise," Obama said. "But when Governor Romney and his allies in Congress tell us we can somehow lower our deficit by spending trillions more on new tax breaks for the wealthy -- well, you do the math. I refuse to go along with that. And as long as I'm president, I never will."

He delivered a forceful defense of his record, but at the same time he asked for patience, invoking Franklin D. Roosevelt's efforts to bring the U.S. out of the Great Depression -- "the only crisis worse than this one."

"I won't pretend the path I'm offering is quick or easy. I never have," Obama said. "You didn't elect me to tell you what you wanted to hear. You elected me to tell you the truth. And the truth is, it will take more than a few years for us to solve challenges that have built up over decades."

And he made the case for an active government, saying recovery "will require common effort, shared responsibility, and the kind of bold, persistent experimentation that Franklin Roosevelt pursued."

Republicans have lambasted Democrats for looking to government to solve problems, and Obama included a caution to his own side, noting that it "should remember that not every problem can be remedied with another government program or dictate from Washington."

He sought to use his platform -- a major prime-time speech attracting possibly 40 million viewers across the country -- to woo the last undecided voters at a time when campaign officials said Americans were just starting to pay attention after returning from their summer vacations and Labor Day holidays. As he arrived on stage, the crowd broke into chants of "Four more years" and waved blue "Forward" signs.

Hour after hour Thursday, delegates heard praise of Obama's accomplishments -- his actions to stabilize the economy, passage of health care legislation that Democrats have sought for decades, the rescue of the auto industry and the killing of Osama bin Laden.

Obama's message, though, could be eclipsed Friday by the release of an August jobs report that's not expected to be a vast improvement over the sluggish growth that has dogged his administration and kept the unemployment rate stuck firmly at over 8 percent for 42 months of Obama's term.

Obama sought to excite his base hours before his address, apologizing via conference call to thousands of disappointed supporters who held tickets for a scrapped outdoor stadium address.

"I need you to remember that nothing is more powerful than the work that you guys do," he told supporters. "Nothing is more powerful than voices calling for change."

Polls suggest voters are uncertain about Obama's ability to return the U.S. economy to full health, and he promised a speech "laying out what are the stakes in this election and what my vision for the future is."

Obama's speech capped a three-day Democratic convention that was not without mishaps. A flap over a decision to strip from the party platform -- and then reinsert -- the word "God" and language that asserts Jerusalem is the capital of Israel, threatened to overshadow much of the message and embroiled senior party officials in a no-win political battle.