WASHINGTON — A flurry of last-minute moves by the House, Senate and White House late Monday failed to break a bitter budget standoff over President Obama’s health care law, setting in motion the first government shutdown in nearly two decades.

The impasse meant that 800,000 federal workers were to be furloughed and more than a million others would be asked to work without pay. The Office of Management and Budget issued orders shortly before the midnight deadline that “agencies should now execute plans for an orderly shutdown due to the absence of appropriations” because Congress had failed to act to keep the federal government financed.

After a series of rapid-fire back and forth legislative maneuvers, the House and Senate ended the day with no resolution, and the Senate halted business until later Tuesday while the House took steps to open talks. But Harry Reid, the Senate majority leader, dismissed as game-playing the House proposal to begin conference committee negotiations.

“We will not go to conference with a gun to our heads,” he said, demanding that the House accept the Senate’s six-week stopgap spending bill, which has no policy prescriptions, before negotiations begin.