A week after announcing a plan to overhaul the reeling retailer, Sears Holdings has announced that Aylwin Lewis will step down as chief executive.

He will be replaced on an interim basis by W. Bruce Johnson, the company's executive vice president for supply chain and operations, who joined Sears from Carrefour in 2003. Sears will start a search for a permanent C.E.O.

The changes come as Eddie Lampert, the hedge fund manager who controls Sears, is scrambling to make his two-year experiment with a merged Sears and Kmart work. Sales have slumped and Sears' stock price has been sliding—down nearly 40 percent last year.

That's a problem for Lampert's main $15 billion hedge fund, which consists largely of Sears stock. He will have to answer to his hedge fund investors next month.

And, as Jesse Eisinger noted in his examination of Lampert's failed tinkering with Sears in Condé Nast Portfolio, there is more at stake here:

"Once hailed as the Warren Buffett of his generation, Lampert, at 45, now has another turnaround job on his hands: his own reputation."

Attracting retailing talent to Sears will be crucial in light of the new approach the company is taking. Sears said last week that it would restructure itself into five business units, each with a designated chief.

Mr. Lampert said, "As we realign Sears into five different types of focused business units, we will be redefining how our leaders operate by giving them greater autonomy and accountability for their businesses. We intend to put in place an operating model that allows managers to act with the flexibility and speed required in today's dynamic and highly competitive marketplace."

The departure of Lewis will follow other recent exits by black C.E.O.'s of prominent American companies. Last year, Stan O'Neal was forced out at Merrill Lynch, while Richard Parsons retired as head of Time Warner.