Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told the panel sequestration would "severely limit our ability to implement our defense strategy," "put the nation at greater risk of coercion" and "break faith with men and women in uniform."
He called for the "antithesis of sequestration -- a steady, predictable funding stream."
"We can do better. Our nation, our service members and their families expect us to do better," Dempsey said. "More importantly, a turbulent world that relies on American leadership demands that we do better."
Gen. Ray Odierno, Army chief of staff, said he's been in the service for 36 years and knows what it takes to "send soldiers into combat."
"And I've seen first-hand the consequences when they are sent unprepared," Odierno said. "I began my career in a hollow Army. I do not want to end my career in a hollow Army."
He said the Army is facing an "unprecedented" and "dire" situation for the 2013 fiscal year.
"In addition to the $170 billion in cuts to the Army levied by the Budget Control Act of 2011, the combination of the continuing resolution, a shortfall -- excuse me -- the shortfall in overseas contingency operations funds for Afghanistan, and the sequester in fiscal year 2013 has resulted in a $17 billion to $18 billion shortfall to the Army's operation and maintenance accounts, as well as additional $6 billion cut to other programs," he said. "All of this will come in the remaining seven months of this year.
"The fiscal year '13 fiscal situation will have grave and immediate readiness impacts on all forces not serving in Afghanistan or forward in Korea -- impacts which will have a significant impact well into fiscal year '14 and beyond."
He said the Army would have to curtail training for 80 percent of its ground forces and furlough up to 251,000 civilians for up to 22 days plus postpone equipment maintenance and halt modernization efforts.
More personnel cuts would come in 2014, he said.
Adm. Mark Ferguson, vice chief of naval operations, rattled off a laundry list of ship construction and upgrade projections that would be put on hold if sequestration occurs.
"We will immediately erode the readiness of the force," Ferguson said. "Over the long term, the discretionary budget caps under sequestration will fundamentally change our Navy. We will be compelled to reduce our force structure, our end strength and investments as we lower funding levels in the altered landscape of our industrial base."
He also warned of the "corrosive effect" budget uncertainty has on morale.
Committee Chairman Carl Levin, D-Mich., noted some members of Congress and the media have supported letting the impending sequestration take effect to severely cut the budget rather than to work out a compromise deficit reduction agreement.
"I could not disagree more. Sequestration is arbitrary and irrational. It will not only weaken our security but, as Secretary [Leon] Panetta said, quote, 'It's not just defense, it's education, loss of teachers, it's child care. It's food safety. It's law enforcement. It's airport safety.'"
Sen. Jim Inhofe, R-Okla., the panel's ranking GOP member, reminded everyone there are just 16 days left until sequestration is to take effect, "16 days that will define our military strength for the coming decades."
He said he and other Republican senators introduced a bill to mitigate the impact of sequestration through the end of the fiscal year and provide the department with the flexibility "it desperately needs to operate under a continuing resolution."
"It's not a perfect solution, but it is better than doing nothing," Inhofe said.
"There is a growing concern that the president will not seriously negotiate with Congress on a compromise to sequestration until after it takes place on March 1."
Sen. John McCain, R-Ariz., likened the situation facing Congress and the country to "a kind of Orwellian experience" with "draconian cuts" in the offing while North Korea tested another nuclear bomb, Iran is "unraveling" and many other hot spots such as Libya, Mali, Egypt and Tunisia demand attention.
"We are probably in a more unsettled period since the end of the Cold War that certainly I have ever seen," McCain said.
"Meanwhile, we are now -- the signal we are sending, frankly, to the Iranians is, 'Don't worry, this aircraft carrier is not coming.' This is really a disconnect the likes of which I have never seen before."
He said it is "disgraceful" to put service men and women through such budget uncertainties and put a shot across President Obama's bow, saying "we elect presidents for a reason, and that's to lead."
"It seems to me that it's now time for the president of the United States to call the leaders of Congress over to the White House and say, 'Look, if you accept the word of every one of our military leaders as to the effect of sequestration; if you accept the fact that the world is more -- becoming more and more dangerous, that this is the worst time, and we should sit down and come to an agreement to prevent the sequestration, if only -- not only for our national security, but for the benefit of the men and women who are serving this nation.'"
Sen. Claire McCaskill, D-Mo., made a point of noting top Republicans were among 28 GOP senators who voted for the sequestration and "we all knew that there would come a day of reckoning, that we would have to sit down and compromise."
"We will not avoid the sequester if we just gonna all draw lines in the sand and say, we're not cutting anything, or we're not going to do any revenue," she said.
"So sign me up for the compromise for painful cuts and for some revenue."
She had a place to find some additional revenue.
"I think that, you know, we've got money right now we're paying out to farmers that we all acknowledge is a huge waste -- waste of money, billions of dollars that ... isn't really going to farmers, and they're getting paid for -- whether they're making a lot of money or not making a lot of money," she said.