New Defense Secretary Chuck Hagel vowed on Friday to preserve U.S. military effectiveness despite $46 billion in new defense cuts he said would jeopardize the Pentagon's ability to fulfill its missions effectively.

Hagel, appearing at his first Pentagon news conference since taking office on Wednesday, said the cuts meant that four U.S. Navy air wings would gradually stop flying, the Air Force would immediately cut flying hours and the Army would reduce training.

"Let me make it clear that this uncertainty puts at risk our ability to effectively fulfill all of our missions," Hagel said, adding that while the cuts remained in effect, "we will be forced to assume more risk, with steps that will progressively have far-reaching effects."

Officials said later that idling an air wing would affect about 70 planes and some 2,500 service members.

While warning about the impact of the cuts, Hagel struck a more moderate tone than many other defense officials, who have said the spending reductions would be devastating or could turn the U.S. military into a second-rate power.

"America ... has the best fighting force, the most capable fighting force, the most powerful fighting force in the world," he said. "The management of this institution, starting with the Joint Chiefs, are not going to allow this capacity to erode."

"We will manage these issues. These are adjustments. We anticipated these kinds of realities, and we will do what we need to do to assure the capabilities of our forces," Hagel said.

The secretary's remarks came as the White House and Congress failed to reach a deal to avert $85 billion in looming cuts to defense and non-defense spending before a midnight deadline.

If no deal has been reached, President Barack Obama is required to notify Congress that "sequestration" has been triggered. That would mean the Pentagon has to slash $46 billion in spending through the end of the fiscal year on Sept. 30.

The country's biggest defense contractor, Lockheed Martin , said it was working to understand how it would be affected by the cuts and would "urge our government leaders to reverse this action and establish a more rational fiscal strategy."

"Any significant delay in funding for any production program could threaten the stability of our supply chains, increase costs, prolong delivery schedules and ultimately weaken our national security posture," the company said in a statement.

'THIS IS NOT SUBTLE'

Republican lawmakers on the House of Representatives Armed Services Committee decried the defense spending cuts and blamed President Barack Obama for the failure to reach a deal to offset them, saying he insisted on raising taxes to replace the cuts.

"It's a crazy way to do things," said Representative Buck McKeon of California, the panel's chairman. "The president promised it would never happen. ... It happened."

"It is unconscionable for this president to use our military families as pawns in his crusade for higher taxes," said Representative Martha Roby of Alabama.

Obama blamed Republicans in his remarks on the cuts, noting the Pentagon was having to figure out how to ensure the children of military families would be able to go to school since the teachers at base schools might be put on unpaid leave.

Hagel said the Pentagon would place a priority on protecting spending for the Afghanistan war.

"The Army will curtail training for all units except those deploying to Afghanistan, adversely impacting nearly 80 percent of Army operational units," he said.

Hagel said the department would issue preliminary notification later this month to thousands of civilian employees who will be required to take unpaid leave.

Officials have said most of the department's 800,000 civilians would be affected, probably being asked to take a day off each week for 22 weeks beginning in April.

Deputy Defense Secretary Ashton Carter said the spending reductions would have a rolling impact, beginning slowly and increasing as the weeks pass.

"Those who do not appreciate how serious this is, as the year goes on, it will be unmistakable," he told the briefing. "This is not subtle. This is an abrupt serious curbing of activity in each and every one of our key categories of activity in the Department of Defense."