A plot of Wall Street interests to overthrow President Roosevelt and establish a Fascist dictatorship, backed by a private army of 500,000 ex-soldiers and others, was charged by Major Gen. Smedley D. Butler, retired Marine Corps officer, who appeared yesterday before the House of Representatives Committee on Un-American Activities, which began hearings on the charges. [The committee] heard testimony from General Butler and Gerald P. Maguire, a bond salesman in the Stock Exchange firm of Grayson M.P. Murphy & Co., 52 Broadway, named by General Butler as having urged him to head the proposed Fascist army. There were immediate emphatic denials by the purported plotters. From Philadelephia came word that General Butler had told friends there that General Hugh S. Johnson, former NRA administrator, was scheduled for the role of dictator, and that J. P. Morgan & Co. as well as Murphy & Co. were behind the plot.