WASHINGTON (AP) — Looming across-the-board budget cuts present the U.S. military with the most significant readiness crisis in more than a decade and quick action is needed to avoid the spending reductions, Defense Secretary Leon Panetta warned during testimony Thursday before the Senate Armed Services Committee.

If the billions of dollars in cuts are allowed to stand, Panetta said, he would have to throw the country's national defense strategy "out the window," and the United States would no longer be a first-rate power. "This will badly damage our national defense and compromise our ability to respond to crises in a dangerous world," Panetta said.

But Panetta assured lawmakers the Defense Department would take the steps necessary to deal with possible threats in the Persian Gulf region after he approved the Navy's request to halve its aircraft carrier presence in the area.

Anticipating the Defense Department will have less money to spend, Panetta said the Pentagon has already put in place a freeze on hiring and cut back on maintenance at bases and facilities. Those moves are reversible, he said, as long as Congress acts quickly to head off the cuts, known as sequestration, and approves a 2013 military budget.

The potential for sequestration to kick in on March 1 is the result of Congress' failure to trim the deficit by $1.2 trillion over a decade. The Pentagon faces a $42.7 billion budget cut in the seven months starting in March and ending in September. The reductions through sequestration would be in addition to a $487 billion cut in defense spending over the next ten years mandated by the Budget Control Act passed in 2011.

Panetta said that the department understood that it needed to do its part to help deal with the federal deficit and has been working to adjust its plans to deal with the lower spending levels. But adding sequestration on top of that creates an untenable situation, he said.

As "time went on and the erosion that would take place in our capabilities, instead of being a first-rate power in the world, we'd turn into a second-rate power," Panetta told the committee. "That would be the result of sequester."

Panetta, who is retiring soon from his post, has been leading a vocal campaign to stop sequestration because it would leave the military "hollow," meaning the armed forces would look good on paper but would lack the training and equipment they need to handle their missions.

As part of that campaign, the Defense Department has been providing greater details on the impact of the cuts. The department on Wednesday said it is cutting its aircraft carrier presence in the Persian Gulf region from two carriers to one, a move that represents one of the most significant effects of sequestration. The U.S. has maintained two aircraft carrier groups in the Gulf for much of the last two years.

The deployments of the USS Harry S Truman and the USS Gettysburg, a guided-missile cruiser, are being delayed as part of the Navy's plan to deal with the budget uncertainty.

Former Defense Secretary Robert Gates decided in 2010 to keep two carrier groups in the Gulf region as tensions with Iran escalated. Iran has repeatedly threatened to close the Strait of Hormuz, a strategic waterway through which roughly a fifth of the world's oil supply passes, in retaliation for increased Western-led sanctions.

"We're going to do everything we can to make sure that we are prepared to deal with the threat from Iran," Panetta said. "We will have one carrier there and we will deploy other forces there so that we can hopefully fill the gap."

Congress has not approved a defense budget for the 2013 fiscal year. Lawmakers have instead been passing bills called continuing resolutions to keep spending levels at the same rate as last year. That means the Pentagon is operating on less money than it planned for, and that compounds the problem, Panetta said.

"We have got to end the cloud of budget uncertainty that hangs over the Department of Defense and the entire U.S. government," Panetta said.

A group of Republican lawmakers from House and Senate have offered a plan to cut the federal workforce and use the savings to replace the cuts to the Pentagon and to domestic programs, which also are affected by the sequester. Similar legislation offered last year did not pass.

Each of the military branches have described in detailed memos to Congress widespread civilian furloughs, layoffs and hiring freezes that will hit workers all around the country. Overall, the Pentagon will furlough 800,000 civilian workers for 22 days, spread across more than five months, and will lay off as many as 46,000 temporary and contract employees, according to the correspondence.

The Navy said it will cease deployments to South America and the Caribbean and limit deployments to Europe. The Air Force warned that it would cut operations at various missile defense radar sites from 24 hours to eight hours. The Army said it would cancel training center rotations for four brigades and cancel repairs for thousands of vehicles, radios and weapons.

There is also concern that the readiness levels of the U.S. nuclear force could be degraded. The Air Force general responsible for maintaining the nation's fleet of nuclear-capable bombers said Wednesday that the possibility of sequestration and smaller defense budgets has lead his command to make a 10 percent cut in flying hours for the B-52 bomber, a long-range aircraft that has been in operation since the 1950s.

"At the wing and the squadron level, they can probably manage that for a little while, and then we'll have to see what the impact of that is," said Lt. Gen. James Kowalski, commander of the Global Strike Command at Barksdale Air Force Base, La.

The B-52, which is the bomber fleet's workhorse, is already flying 20 percent fewer training missions than it did in 2001, according to Kowalski.

Kowalski also said discussions among senior national security officials are under way to determine whether missions handled by the nation's nuclear forces should get priority budget status in the event of sequestration. Global Strike Command also is responsible for B-2 stealth bombers and intercontinental ballistic missiles.