WASHINGTON — For weeks, President Barack Obama has warned of the dire consequences of allowing the automatic across-the-board spending cuts known as sequestration to go into effect.

The nation would be more likely to sustain a terrorist attack. Criminals would be set free. Schoolteachers would be laid off by the thousands.

“If Congress allows this meat-cleaver approach to take place, it will jeopardize our military readiness; it will eviscerate job-creating investments in education and energy and medical research,” Obama said last week.

But his warnings didn’t spur Congress to act. And the White House had to respond to questions about whether it inflated the claims of danger.

Facing a barrage of questions Thursday, White House spokesman Jay Carney said the administration was “very confident” about the accuracy of its warnings. He blamed reporters for saying that repercussions would be immediate and claimed that Republicans had switched their political strategy to downplay the effects of the cuts. “I can tell you that the impacts … are real,” he said.

Carney cited a report from the nonpartisan Congressional Budget Office that indicates the reductions would slow the economy and cost hundreds of thousands of jobs.

“If this happens, you should go out to Ohio and ask the families that are affected if they think it’s real,” he said. “Ask the family whose child will not have a slot in Head Start whether they think it’s real. Ask the civilian Defense Department employee, who’s already gotten a notification that he or she will be furloughed, whether that has a real impact.”

But Carney couldn’t explain why Education Secretary Arne Duncan said this week that Kanawha County, W.Va., had already issued layoff notices in anticipation of the cuts when the layoffs had nothing to do with the possible reductions.

The effects of many cuts would not be felt for months, maybe not until next year, as local and state agencies figure out how to make do with less. While the federal government might not have much flexibility in how it dispenses the cuts, local agencies may be able to shift money around to try to accommodate them.

“On Monday we’ll be able to police the streets,” said New York Mayor Michael Bloomberg, who visited the White House this week. “There will be a fire engine that responds and an ambulance. Our teachers will be in front of the classroom. If there’s snow we’ll be able to plow. It’s something that takes awhile to implement,” he said.

“There’s a lot of posturing: ‘I’m going to lay off my employees today unless you do something. We’re going to close the hospitals down. We’re going to take all the prisoners from jail and put them on the streets.’ Spare me. I live in that world. I mean, come on, let’s get serious here,” Bloomberg said.

Obama appeared to hedge his warnings this week.

“I should point out, and I’m sure you’ve heard from a number of experts and economists that this is not a cliff, but it is a tumble downward,” he told the Business Roundtable on Wednesday night. “It’s conceivable that in the first week, the first two weeks, the first three weeks, the first month . . . a lot of people may not notice the full impact of the sequester.”

Carney said the White House wasn’t toning down its warnings because of concern that it had overstated the impact.

“It’s our responsibility to be upfront about the fact that you cannot responsibly cut $85 billion out of the budget in seven months without having dramatic effects on the defense industry and civilian workers, on our national security readiness, on teachers, on kids in Head Start,” he said.

The reductions probably will start going into effect today if Republicans and Democrats on Capitol Hill do not make a deal to stop them.

Republicans want to keep the same level of cuts but allow the government to choose where to trim. Democrats want to pass a package of smaller spending reductions and additional tax revenue. Democrats rejected the offer of flexibility, saying it wouldn’t help.