With President Clinton poised to sign the Financial Services Modernization Act, New York attorneys representing financial institutions are preparing for an onslaught of legal work as banks, securities firms and insurance companies evaluate how best to structure their organizations and expand the products and services they offer.

The landmark legislation, passed by Congress Thursday, will set the stage for the creation of financial holding companies that can provide consumers with an extensive portfolio of services, ranging from bank loans to investments to insurance policies. It will also free banks to become much bigger players in the securities business, and allow insurance companies to own banks that accept commercial deposits.