Should the United States send an ambassador to the Vatican? The question has echoed up and down the country since President Truman made his last-minute appointment of General Mark Clark in the closing hours of the Eighty-second Congress. PAUL BLANSHARD, who spent the year 1950 in Rome, believes that such an appointment violates the traditional American principle of equality of all religions before the state, and special treatment for none. He is the author of two widely read books: American Freedom and Catholic Power and Communism, Democracy, and Catholic Power.