An investor is seeking a stake in Rothschild.

L. F. Rothschild, Unterberg, Towbin, a closely held Wall Street investment banking house, confirmed that it is considering an offer from an investment group led by Marshall S. Cogan to buy as much as 50% of the firm. If completed, the purchase would mark the return of Cogan to Wall Street after more than a decade. It also may be an attempt by Cogan to develop a stronger base for launching corporate takeover raids, according to Wall Street executives who follow his activities.