“ Whenever the President determines that any real property acquired under this title and retained is no longer needed for the defense of the United States, he shall if the original owner desires the property and pays the fair value thereof, return such property to the owner. In the event the President and the original owner do not agree as to the fair value of the property, the fair value shall be determined by three appraisers, one of whom shall be chosen by the President, one by the original owner, and the third by the first two appraisers ”