Defense Secretary Chuck Hagel on Wednesday defended the Pentagon’s proposed budget from criticism by Senate Republicans who said that steep cuts envisioned in the plan would leave the United States vulnerable in an increasingly chaotic world.

The Obama administration plans to slash defense spending to about $495 billion in 2015, or about $113 billion less than the levels contemplated in last year’s budget proposal.

“The results of these cuts have been devastating to our national security,” said Sen. James M. Inhofe (Okla.), the ranking Republican on the Senate Armed Services Committee.

The cuts are the product of a bipartisan budget deal that enacts discretionary spending caps that aren’t especially popular with the Pentagon or lawmakers of either party.

Hagel described the big reductions in spending as necessary to protect training budgets for the current force and to preserve money set aside to buy new planes, ships and ground combat vehicles.

“We will continue investing in high-end ground capabilities to keep our soldiers the most advanced on Earth,” he said in testimony before the Senate panel.

Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, said that even with the cuts, the military would still be able to carry out its missions around the globe, albeit with increased risk.

The cuts will hit ground ­forces especially hard, scaling back the Army to about 440,000 troops, its smallest size in 74 years. Only a few areas, such as Special Operations and cyber ­forces, will see modest increases under the budget proposal.

The Republican criticism of the spending plan was muted somewhat because both parties had signed off on the current budget caps.

“You come here with a budget that constrains us in a way that is unprecedented,” said Sen. John McCain (R-Ariz.). McCain also noted that the challenges the Pentagon faces “have been bred by sequestration,” the law that put in place the initial automatic spending caps.

The Obama administration’s long-term budget plan seeks to increase Pentagon spending by as much as $35 billion beyond the current caps in 2016 and an additional $80 billion from 2017 to 2020. The future increases in spending are likely to face stiff resistance from budget hawks in both parties.

“I think [the increases] are wishful thinking,” said Todd Harrison, an analyst with the Center for Strategic and Budgetary Assessments in Washington.

Hagel emphasized that without the extra spending, starting in 2016, the military’s ability to execute the administration’s strategy would be “seriously jeopardized” and put at risk “America’s traditional role as a guarantor of global security, and ultimately our own security.”