WASHINGTON -- President Barack Obama said today that "the hour for immediate action is here" on a deal to avert the "fiscal cliff."

The president, at a White House press briefing, said he remained "optimistic" that an agreement can be reached in Congress before a looming year-end deadline to avoid tax increases and spending cuts.

If Congress can't reach a deal, the president said Congress should allow a vote on a basic package that would preserve tax cuts for middle-class Americans while extending unemployment benefits for the long-term jobless and working toward a foundation for a broader deal.

Obama described an hourlong meeting Friday with congressional leaders Friday as "good and constructive."

The end game at hand, the White House and Senate leaders launched a final attempt at compromise Friday night in hopes of preventing a toxic blend of middle-class tax increases and spending cuts from taking effect at the turn of the new year.

Senate leaders say they hope to reach a compromise that could be presented to lawmakers by Sunday, little more than 24 hours before the deadline.

Senate Majority Leader Harry Reid and GOP leader Sen. Mitch McConnell also gave a relatively upbeat assessment after the duo and top House leaders had what McConnell called a "good" meeting with Obama on Friday.

"I am hopeful and optimistic" of reaching an agreement after months of gridlock, said McConnell.

Reid said, "I'm going to do everything I can" to prevent the tax increases and spending cuts that threaten to send the economy into recession. He cautioned, "Whatever we come up with is going to be imperfect.

Success was far from guaranteed in an atmosphere of political mistrust -- even on a slimmed-down deal that postponed hard decisions about spending cuts into 2013 -- in a Capitol where lawmakers grumbled about the likelihood of spending the new year holiday in the Capitol.

"The clock is ticking," Sen. Max Baucus, chairman of the Senate Finance Committee, said in remarks on the Senate floor as Obama and congressional leaders were meeting several blocks away at the White House. "My message to them is simple. We can do this. We can get this done, and we must," added the Montana Democrat.