A top Pentagon official assured South Koreans Wednesday that the size and operation of American forces on the peninsula will remain intact despite plans to make deep cuts in the number of U.S. ground troops.

"The importance of our relationship with Korea and the importance of our commitment to South Korea and the troops on the peninsula is not affected by our plans," Christine Fox, acting deputy secretary of defense, said at a forum here hosted by American Economic Institute.

It is a matter of Washington's strategic imperative and "there will be no impact at all on our agreements or commitments to Korea," she added.

Her remarks came a couple of days after Secretary of Defense Chuck Hagel made public plans to downsize the Army as part of efforts to adjust to the era of federal budget constraints.

Under the proposal, the Army will be downsized to between 440,000 and 450,000 soldiers by 2017. The current force is 520,000.

The department will also retire the Air Force's U-2 spy plane and A-10 attack aircraft.

Fox said the challenge for the smaller Army is believed to be "manageable."

Army Chief of Staff Gen. Ray Odierno would prefer more flexibility, she added.

"But it gives him enough flexibility to meet the requirements that any Korean contingency would require and sustain our commitment to the forces on the peninsula," she said.

On the upcoming retirement of U-2, Fox emphasized that the operations and sustaining costs of the new version of Global Hawk surveillance aircraft have significantly come down.

South Korea is moving to purchase four Global Hawk Block 30 unmanned planes in the coming years. (Yonhap)