WASHINGTON — The federal government began a partial shutdown last night as House Republicans insisted that any measure to finance the government during the next couple of months include revisions in the new health-care law, much of which goes into effect today.

With the Democrat-majority Senate unwillingly to agree to such a demand, the White House Office of Management and Budget ordered federal departments to begin shutting down at midnight last night.

After a series of back-and-forth legislative maneuvers, leaders of the House and Senate acknowledged early today that there would not be a resolution in time to stop a shutdown, even as the House took steps to open talks. But Harry Reid, the Senate majority leader, dismissed as game-playing a late 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. The Senate then announced its plan to recess until 9:30 a.m. today.

Shortly before 9 p.m. last night, the House approved by a vote of 228-201 a temporary spending measure that also would delay for one year the health-care law’s requirement that all Americans have a health-insurance policy or face a federal fine.

The House proposal also would have denied federal subsidies to members of Congress, the Capitol Hill staff, executive-branch political appointees, the White House staff and the president and vice president, who would be forced to buy their health coverage on the Affordable Care Act’s new insurance exchanges.

In less than an hour, the Senate killed the House bill by a 54-46 vote and sent the stopgap spending bill right back, free of policy prescriptions. Earlier in the day, the Senate had taken less than 25 minutes to convene and dispose of a similar weekend budget proposal by House Republicans.

“They’ve lost their minds,” Reid, D-Nev., said before disposing of the House bill the second time. “They keep trying to do the same thing over and over again.”

President Barack Obama spoke by telephone earlier in the evening with House Speaker John Boehner, R-West Chester. Aides to Boehner said the call lasted about 10 minutes.

But Obama and Reid made it clear that they would not agree to House Republicans’ demands that the health law, dubbed Obamacare, be altered as a price for their support of financing the government.

The federal spending year ended last night, and Congress had not agreed on any of the 13 spending bills to finance the government for the new fiscal year that begins today.

After Congress missed its midnight deadline, Obama addressed U.S. troops in a three-minute video message. He told them that troops in uniform will remain on duty as usual, and that he had signed a law yesterday to ensure they get their paychecks on time.

That measure began as a GOP bill in the House and was taken up by the Senate, reflecting a rare measure of agreement among Democrats and Republicans: No one wants to be blamed for the military not getting paid.

Of the shutdown, Obama told the troops: “Unfortunately, Congress has not fulfilled its responsibility. It has failed to pass a budget and, as a result, much of our government must now shut down until Congress funds it again.”

Thousands of civilians who work for the Defense Department face furloughs, compounding the damage already inflicted on the military by automatic spending cuts.

Hundreds of thousands of government workers will be off the job today.

Earlier yesterday, Obama told reporters at the White House that a shutdown would “have a very real economic impact on real people, right away. Past shutdowns have disrupted the economy significantly. This one would, too. It would throw a wrench into the gears of our economy at a time when those gears have gained some traction.”

“You don’t get to extract a ransom for doing your job,” Obama said.

The impasse wasn’t closing the entire government. Social Security checks are to be mailed, Medicare patients still will be able to see physicians or go to a hospital, and the mail will be delivered.

But more than 800,000 federal workers are facing furloughs. In the past, Congress has agreed to pay them retroactively after a shutdown has ended, but the partisan divisions are so deep today that nobody was certain that lawmakers would approve such a measure.

Although polls suggest that more Americans will hold the Republicans responsible for a partial shutdown than the Democrats, House Republicans were doing their best last night to argue that Reid was goading the GOP into a shutdown.

“At some point in time the American people are going to see this guy doesn’t want to compromise,” said Rep. Pat Tiberi, R-Genoa Township.

But a Republican lobbyist who spoke only on the condition of anonymity warned that GOP lawmakers on Capitol Hill simply will not be able to match Obama’s ability to reach millions of voters.

“You just can’t compete with the president’s megaphone,” he said. “That’s the challenge for Republicans.”