"That's the big question," Democratic Sen. Mark Udall of Colorado, a member of the Senate Armed Services Committee, told CNBC. "The president always proposes, and Congress always disposes."
Contractors and weapons
Hagel's budget reduces or suspends purchases of some big contractors' weapons systems and preserves others.
Proposed cutbacks include reduced purchases of Predator and Reaper drones from privately held General Atomics Aeronautical Systems, and a plan for no further orders of littoral combat ships, which are made by Lockheed Martin and General Dynamics.
(Read more: Fear of losing tech edge factors into Pentagon budget plans)
At the same time, Hagel would preserve funding for multibillion-dollar equipment development programs, such as Lockheed's F-35 Joint Strike Fighter and a long-range bomber program that is expected to be the target of competing bids from a joint Lockheed-Boeing team and a Northrop Grumman team.
The Obama administration has proposed to make troop cuts through a drawdown in Army personnel, from more than 520,000 soldiers to about 450,000 by 2019.
According to Christopher Preble, vice president for defense and foreign policy studies at the Cato Institute, the budget represents a shift from a large military ground force characterizing an era of overseas wars in Iraq and Afghanistan to a smaller, more highly trained force that makes greater use of technology.
(Read more: FACT BOX—How Pentagon's 2015 budget affects key weapons programs)
"If we're not doing low-tech wars that require boots on the ground, you have a smaller, elite force that allows you to use technology and train some exceptionally skilled people," he said.
While some have voiced disapproval of the budget, especially its reductions in military personnel and possible cuts to benefits, such as subsidized grocery prices, Preble sees limited room for adjustment given restrictions imposed by sequestration.
"They might just accept the unhappy choices and then blame the White House for what comes next," he said of Congress.