Sept. 30, 1962 - At midnight last night, President Kennedy committed the full weight of the Federal Government to end Mississippi’s defiance of the Union. He called the state’s National Guard into Federal service. He sent U.S. Army troops to Memphis, Tenn., to stand in reserve if more force were needed. And he issued a proclamation calling on the Government and people of Mississippi to abandon what had become the most serious challenge to Federal authority since the Civil War. Tonight, the President will explain the situation to the American people. He will speak over all national T.V. and radio networks at 7:30 New York time. The President took what one official called his “irrevocable steps” after three telephone conversations yesterday with Governor Ross R. Barnett of Mississippi. In the conversations, the President was unable to receive from Governor Barnett any satisfactory assurances that law and order could, or would, be maintained in Oxford, Miss., during the coming week. Oxford is the seat of the University of Mississippi. Mississippi’s defiance of Federal court orders to admit a Negro, James H. Meredith, to the university has provoked the crisis.