WASHINGTON (AP) -- President Barack Obama declared a debt-crisis session Thursday with congressional leaders was "very constructive" but said the parties were still far apart on deficit reduction proposals. He said he would reconvene the negotiators on Sunday.

Thursday's meeting came amid signals that the White House was willing to reduce costs for major benefit programs including Social Security and Medicare, while Republicans indicated they might consider new steps to raise government revenue.

"People were frank," Obama said, just moments after adjourning the one-and-a-half hour meeting with the eight lawmakers who make up the bipartisan leadership of Congress.

Obama acknowledged that the ultimate agreement will not satisfy partisans on both sides, but he said the deal would require both Republican and Democratic votes to pass Congress.

"Everyone acknowledged that pain will be involved politically on all sides," he said.

Obama met with the leaders of both parties around a table in the White House Cabinet Room as they struggled to reach a deal on raising the government's debt limit with less than four weeks remaining before a possible first-ever default on U.S. financial obligations. The Obama administration says the government needs to raise the current $14.3 trillion debt limit by Aug. 2.

Returning to the Capitol after the meeting, House Speaker said: "We had a conversation. It was productive."

While discussions on trimming the costs of entitlement programs had centered on Medicare, the health care program for older Americans, the White House is revisiting a proposal raised earlier in the negotiations to change the inflation measurement used to calculate Social Security cost-of-living adjustments, thus reducing annual increases, officials said Thursday.

The White House has also said the president is aiming for deficit reduction closer to $4 trillion over 10 years -- an ambitious number that would nearly double the roughly $2 trillion that had been at the center of negotiations.

Democratic and Republican officials familiar with the discussions said Thursday that Social Security was in the mix for potential cost savings. Reintroducing the retirement program to the talks is likely to cause anxiety among congressional Democrats who have insisted that Social Security does not contribute to the nation's deficit problems. White House spokesman Jay Carney said the same after Obama spoke.

The officials spoke on the condition of anonymity because of the sensitivity of the talks. They stressed that no aspect of the deal had been accepted by either side.

Obama ignored a question about Social Security during a photo session at the beginning of the meeting. Carney also declined to discuss options before the negotiators.