By Joseph A. Giannone

NEW YORK (Reuters) - Goldman Sachs Group (GS.N: Quote, Profile, Research) said on Sunday it had added ArcelorMittal SA (ISPA.AS: Quote, Profile, Research) Chairman Lakshmi Mittal to its board, gaining the help of one of the world's richest men but also creating hurdles for its bankers to overcome to avoid conflicts of interest.

As the chairman and chief executive of ArcelorMittal, Mittal is a dealmaking businessman whose influence now extends far beyond his native India. Mittal and his family strung together a series of acquisitions to create the world's largest steelmaker, responsible for 10 percent of global steel output.

Yet with rivals and critics always on the lookout for conflicts of interest, Goldman's bankers now must go to greater lengths when doing business with ArcelorMittal.

Adding Mittal "creates some hurdles," a Goldman spokesman said.

Certainly this is the kind of client that investment banks are loath to lose. According to Thomson Reuters data, Mittal has been involved in 179 transactions totalling $79 billion (40 billion pounds) over the past decade.

Goldman has advised Mittal on five deals since 2006 totalling $47 billion in volume. Goldman and Citigroup are tied for second place behind Credit Suisse, which since 1998 is the steelmaker's top advisor.

Times have changed since banks eagerly added industrial chiefs to their boards and sent managing directors to serve on the boards of clients. Today, insider dealing rules and heightened worries about conflicts of interest mean banks need to tread more carefully.

Goldman in particular has come under fire since it is the world's largest securities firm and therefore likely to be involved in more deals. The bank also aggressively pursues work as a lender, adviser and investor -- sometimes all in the same transaction.