WASHINGTON, Nov. 23, 1963 (UPI) - Lyndon Baines Johnson today met the awesome responsibilities of President of the United States grimly determined - with the help of God and a united America - to carry on the tasks left him by John F. Kennedy. Less than 24 hours after he formally took office in a hot, stuffy airplane in Dallas, Tex., the new chief executive called in Secretary of State Dean Rusk (at 9:30 a.m. EST) for the first of a full day of top-level meetings. Among other officials, Johnson