SAN FRANCISCO (Reuters) - Hewlett-Packard Co's chief strategy and technology officer has retired, becoming the latest senior executive to leave the storied Silicon Valley giant struggling to restore its tarnished credibility.

Shane Robison, 57, will step down on November 1, ending an 11-year term at the company, which is now pondering a sale or spinoff of its core personal computing division and trying to assure skeptical investors it can restructure to return to growth.

HP appointed former California gubernatorial candidate Meg Whitman CEO just last month, after firing former leader Leo Apotheker for a series of missteps, including a poor run at convincing Wall Street he had not overpaid for British software firm Autonomy Plc.

Robison, a pivotal figure in crafting long-term strategy for the largest U.S. technology company through mergers and acquisitions and research and development, will not be replaced, HP said in a statement.

"Shane has been a powerful innovator for our business groups and other corporate divisions," Whitman said in the statement.

But "in an effort to drive strategy, research and development closer to the company's businesses, it will not be replacing the role of chief strategy and technology officer," HP's statement read.

Shares in the company have plunged 17 percent since August 18, when it announced the $12 billion acquisition of Autonomy and its decision to consider a spinoff of its PC business, the world's largest. HP later acknowledged that the decision to announce may have been premature, and may have alienated some partners.

(Editing by Bob Burgdorfer)