WASHINGTON — The contours of a deal to avert the year-end “fiscal cliff" are becoming increasingly clear. But progress has been slow, and time is running out for leaders to seal an agreement and sell it to restless lawmakers who so far have been given little information.

With hope still alive for a resolution by Christmas, President Barack Obama and House Speaker John Boehner, R-Ohio, met Sunday at the White House, their first face-to-face meeting in nearly a month and their first one-on-one session since July 2011, when they last tried to forge a far-reaching compromise to tame the national debt.

Neither side would provide details, but White House spokeswoman Amy Brundage and Boehner spokesman Michael Steel released identical statements saying that “the lines of communication remain open."

Lawmakers say action this week is vital if Obama and Boehner hope to win approval by the end of the year for complex, bipartisan legislation that would raise taxes, push down social-safety-net spending and lift the federal debt limit.

“We’re getting down to as late as it’s physically possible to actually turn a framework into enactable legislation and then actually get it passed," said Sen. Chris Coons, D-Del., who is anticipating a complicated bill with “many real consequences for average Americans’ lives." He added: “For senators to responsibly vote on a big, bold framework or package, we need time to review, debate and discuss this. And we are rapidly running out of running room."

In recent days, Boehner has called repeatedly on Obama to respond to an offer the GOP laid out last week. By Friday, a frustrated Boehner was complaining that, while the two sides continued to talk, there was “no progress to report."

It was not immediately clear whether that changed Sunday. But with written proposals from both sides now on the table, senior aides say the elements of a deal are coming into focus:

• Fresh tax revenue, generated in part by raising rates on the wealthy, as Obama wants, and in part by limiting their deductions, as Republicans prefer. The top rate could be held below 39.6 percent, or the definition of the wealthy could be shifted to include those making more than $375,000 or $500,000, rather than $250,000 as Obama has proposed.

Obama wants $1.6 trillion over the next decade, but many Democrats privately say they would settle for $1.2 trillion. Boehner has offered $800 billion, and Republicans are eager to keep the final tax figure under $1 trillion, noting that a measure to raise taxes on the rich passed by the Senate this summer would have generated only $831 billion.

• Savings from health and retirement programs, a concession from Democrats necessary to sell tax hikes to GOP lawmakers. Obama has proposed $350 billion in health savings over the next decade. Boehner has suggested $600 billion from health programs and an additional $200 billion from using a stingier measure of inflation, reducing cost-of-living adjustments for Social Security recipients.

• Additional savings sufficient to postpone roughly $100 billion in across-the-board agency cuts set to hit in 2013, known as the sequester, and to match a debt-limit increase. The sequester, perhaps paired with an automatic tax hike, could then serve as a new deadline, probably sometime next fall, for wringing additional revenue from the tax code and more savings from entitlement programs.