Mitchell Disbarred As Lawyer in State
Ex-Atty Gen John N Mitchell, who was convicted of perjury and conspiracy to obstruct justice in Watergate scandal, is disbarred from practicing law in NYS; his disbarment is believed to be 1st in history of US of a lawyer who held such high office; Mitchell argues action should not be taken until his appeals are exhausted; rev of Mitchell-Nixon relationship and Mitchell's conviction; Mitchell illus (M)