Update: The Department of Defense announced on Monday that Secretary of Defense Chuck Hagel will deliver remarks on the Army's future force structure on Tuesday at 4 p.m.
WASHINGTON (CNN) - A scaled-back, modern U.S. military would cut the Army to its pre-World War II size and do away with the A-10 "Warthog" attack jet, Defense Secretary Chuck Hagel will say Monday in proposing a new budget to reflect the end of America's longest war.
"After Iraq and Afghanistan, we are no longer sizing the military to conduct long and large stability operations," Hagel will say in announcing his 2015 Defense Department budget plan, according to advance text released by the Pentagon.
Downsizing due to modernization and budget constraints began under Hagel's predecessor, Robert Gates, and the proposal described Monday began a new phase of the change.
"As we end our combat mission in Afghanistan, this will be the first budget to fully reflect the transition DoD is making after 13 years of war -- the longest conflict in our nation's history," Hagel says in the advance text.
The former Republican senator from Nebraska describes a military capable of fighting on one war front and maintaining effective defenses for a second while shifting to a more tactical capability.
"Our analysis showed that this force would be capable of decisively defeating aggression in one major combat theater -- as it must be -- while also defending the homeland and supporting air and naval forces engaged in another theater against an adversary," he says.
Hagel acknowledges the changes mean assuming more risk, but he says the military would better situated to respond to the evolving security challenges facing the country.
"We must maintain our technological edge over potential adversaries," he says, adding that "the military must be ready and capable to respond quickly to all contingencies and decisively defeat any opponent should deterrence fail."
The recommendations in the budget plan for 2015 and ensuing years "favor a smaller and more capable force -- putting a premium on rapidly deployable, self-sustaining platforms that can defeat more technologically advanced adversaries," Hagel says, adding that they also include "important investments to preserve a safe, secure, reliable, and effective nuclear force."
In the proposal, Hagel calls for cutting the Army to a level of 440,000 to 450,000 troops, which would be the lowest level in more than 70 years. At its height, the Army had 570,000 troops after the September 11,2001, terrorist attacks.
According to Hagel, the budget proposal protects funding for cyberwarfare and special operations, and preserves funding for the controversial and costly F-35 fighter jet.
His plan would retire the A-10, which Hagel called a 40-year-old, single purpose aircraft, at a cost savings of $3.5 billion over five years.
The proposed cuts are certain to come under sharp criticism in Congress, especially from legislators with large military bases or contractors in their states and districts.
Republican hawks have battled the military force reductions that are part of President Barack Obama's attempts to reduce defense spending as part of overall deficit reduction.
Hagel warns that if Congress fails to eliminate planned across-the-board spending cuts in future years, the military reductions will be on a greater scale.
Some of those forced cuts, known as sequestration, were eased for this year and next under the budget deal worked out by Congress in December.
Details of Hagel's proposal were first reported by the New York Times.
By Tom Cohen. CNN's Halimah Abdullah contributed to this report.