NEW YORK--Marvin S. Traub, former chairman of Bloomingdale's, Federated Department Stores, is joining Financo Inc., an investment banking firm, as senior adviser. Traub will continue to operate his marketing and consulting firm, Marvin Traub Associates, but will do so from Financo's headquarters. Asked if his new association could lead to a merger of Traub's business into Financo, Traub said, "We'll have to wait and see how things develop. I'm very busy with my own plans." Traub said he will be working for Financo on a project basis, andhis marketing and retail background would benefit the company in its merger negotiations. Gilbert W. Harrison, chairman of Financo, said Traub's international contacts will also be important to Financo's businesses. The firm, which provides financial services to apparel and retailing companies, most recently worked with Federated in its acquisition of Macy's. Financo was also involved in the sale this past year of McRae's to Proffitt's and represents the E.M. Warburg Pincus & Co. group that is acquiring the Petrie Stores Corp.'s retail business. Among Traub's consulting clients are Jones New York, Block Industries, Penn Traffic, Iman Cosmetics and Prime Retail, developers of outlet malls.