Sprint Nextel Corp. announced that Gary Forsee stepped down as chairman and chief executive amid pressure from investors over the wireless carrier’s lackluster performance in recent months.

The chief financial officer, Paul Saleh, will assume the title of acting CEO while the company’s board conducts a search for a replacement. A board member, James Hance, Jr., will take over as non-executive chairman, the company said. As part of his appointment, Mr. Hance will also assume the responsibility of lead independent director previously held by Irvine Hockaday.

Mr. Hockaday, who is staying on the board, said in a statement the company’s search for a CEO is focusing on external candidates.

“We fully expect that the search will be concluded in a timely manner and we are focused on selecting the right candidate to guide the company to achieve its full potential,” Mr. Hockaday said. “Sprint Nextel has the assets, spectrum, customer base, and technology to be the leader in wireless mobility services.”

Sprint also confirmed the fears of some investors who suspected the company’s already poor financial performance in recent months is deteriorating. Sprint said yesterday that it expects to report a third quarter net loss of approximately 337,000 subscribers in the key “post-paid” market segment — customers who sign annual contracts and pay monthly bills.