WASHINGTON - President Obama basked in a series of year-end legislative victories Wednesday, calling them a testament to bipartisanship, but he warned that Democrats and Republicans are likely to lock horns in the next Congress on budget and spending issues.

In a year-end news conference before heading to Hawaii to join his family on vacation, Obama hailed the lame-duck session of the 111th Congress as the "most productive postelection period in decades."

"And it comes on the heels of the most productive two years that we've had in generations," the president said.

Obama's assessment came on a day of major accomplishments that began with his signing of the repeal of the "don't ask, don't tell" ban on gays in the military. That was followed by the Senate's ratification of the administration's nuclear-arms treaty with Russia and Congress' approval of $4.2 billion in aid for first responders who contracted ailments after working at the site of New York's destroyed World Trade Center after the Sept. 11, 2001, attacks.

"One thing I hope people have seen during this lame duck, I am persistent," Obama said. "If I believe in something strongly, I stay on it."

But the president also expressed disappointment over what he did not accomplish: securing long-term funding of the federal government, and getting Congress to pass the DREAM Act, a measure that would offer a conditional path to citizenship to illegal immigrants who were brought to this country as children.

The measure passed the House, but it was blocked by Senate Republicans.

"Maybe my biggest disappointment was the DREAM Act vote," Obama said. "I get letters from kids all across the country, came here when they were 5, came here when they were 8. Their parents were undocumented. . . . The kids don't know. The kids are going to school, like any other American kid."

The president pledged to continue to seek an overhaul of immigration laws next year. At a minimum, he said, "we should be able to get the DREAM Act done."

Obama did not engage in the chest-thumping victory lap that many congressional Republican critics predicted. Instead, he struck a bipartisan pose, repeating his line that he and Democrats suffered a "shellacking" in last month's midterm elections.

"I think what's happened over the last several weeks is it's not a victory for me, it's a victory for the American people," Obama said. "And I hope the lesson that everybody takes from this is that it's possible for Democrats and Republicans to have principled disagreements, to have some lengthy arguments, but to ultimately find common ground to move the country forward."

However, he insisted that he's not "naive" and fully expects fights with Republicans in Congress on the budget, spending priorities, taxes, and issues such as immigration.

He made clear he intends to contest Republicans when the tax bill he just signed comes up for renewal in two years. It extends tax cuts at upper incomes, and the president said he continues to believe that "we can't afford a series of tax breaks for people who are doing very well and don't need it."