WASHINGTON, July 8 (Reuters) - A Pentagon program to

replace some of its aging intercontinental ballistic missiles

will be years behind schedule and 81% over budget, the U.S.

military said on Monday.

The project, now named the Sentinel intercontinental

ballistic missile program, is designed and managed by Northrop

Grumman ( NOC ), and aims to replace aging Minuteman III

missiles.

The program is estimated to cost $140.9 billion, up 81% from

a cost estimate in September 2020.

"We are fully aware of the costs, but we are also aware of

the risks of not modernizing our nuclear forces and not

addressing the very real threats we confront," U.S. Under

Secretary of Defense for Acquisition and Sustainment William

LaPlante told reporters. LaPlante certified that the program

should continue despite the cost overrun.

"There are reasons for the cost growth, but there are no

excuses. We are already working to address the root causes, and

more importantly, we believe we are on the right path to defend

our nation," LaPlante added.

The majority of the cost growth is associated with launch

facilities, launch centers and other processes involved with

converting from Minuteman III to Sentinel. Reuters has reported

that the "unmodified program" cost could be as much as $160

billion.

The new Sentinel cost estimate eclipses an increase to "at

least" $131 billion that the Air Force made public in January.

That triggered the Nunn-McCurdy Act, a 1982 law that

requires the Pentagon to formally justify to Congress the

importance of a program whose unit acquisition costs have risen

more than 25% above a baseline.