(Updates share price in sixth paragraph.)

Oct. 6 (Bloomberg) -- J.C. Penney Co., the department-store operator part owned by investor Bill Ackman, decreased its third-quarter profit forecast after September store sales slumped.

Profit excluding some items will be as much as 15 cents a share in the third quarter, the Plano, Texas-based retailer said in a statement today. Previously, the company forecast earnings of as much as 25 cents. Analysts expected 19 cents a share, the average of three estimates.

J.C. Penney earlier this week named former Target Corp. executive Michael R. Francis president to focus on marketing and planning as the company redefines a chain that had three straight annual sales declines before a gain of 1.2 percent in its fiscal 2011.

Sales at stores open at least a year fell 0.6 percent in September, the company said. The average estimate of analysts surveyed by Retail Metrics was for a gain of 0.9 percent. Same-, or comparable-store sales are considered a key indicator of a retailer’s growth because new and closed sites are excluded.

J.C. Penney is scheduled to report third-quarter earnings before the market opens on Nov. 14.

J.C. Penney rose 78 cents, or 2.8 percent, to $28.42 at 4:15 p.m. in New York Stock Exchange composite trading. The shares have dropped 12 percent this year.

--Editor: Kevin Orland

To contact the reporter on this story: Leslie Patton in Chicago at lpatton5@bloomberg.net

To contact the editor responsible for this story: Robin Ajello at rajello@bloomberg.net.