The brokerage firm filed the suit in federal courts in New York and Houston, charging that the Houston businessmen defrauded it of $48 million by settling an earlier disagreement last year with a promissory note collateralized by worthless stock in two insolvent savings and loan associations. The defendants include Houston mortgage banker George Aubin and J. B. Haralson, the principal of the two thrifts. E. F. Hutton, asking more than $100 million in damages, says it was led to believe that the S&L stock pledged to the promissory note was worth $100 million. In fact, the S&Ls were placed into state conservatorship in March.