The White House and top U.S. lawmakers are engaged in last minute talks to hammer out an agreement to ensure the government has enough money to meet its expenses.

Congress must approve an increase in the government's borrowing authority if the U.S. Treasury Department is to be able to pay the nation's bills. Past increases have been routine, but Republicans in Congress have demanded huge spending cuts with no increase in taxes as a condition for approving the increase in the debt ceiling this time.

Republicans are now calling for an immediate short-term agreement and a revisiting of the debt ceiling debate next year, while Democrats are pushing for a plan to cover the nation's borrowing needs past the presidential and congressional elections in November 2012.

Congress has until Tuesday to raise the country's $14.3 trillion debt ceiling or risk leaving many bills unpaid.

The U.S. Senate is now scheduled to vote on a debt limit proposal Sunday afternoon.

Senate Majority leader Harry Reid said late Saturday the White House had asked him to give everyone as much time as possible to reach an agreement, amid signs there was progress in the negotiations.

If the Treasury runs out of funds, the default on payments could cause interest rates to rise and financial markets around much of the world to sink.