Topeka ? The chairman and chief executive officer of the largest electric company in Kansas plans to retire later this year, and its board of directors has picked one of his top subordinates as his replacement, the utility announced Thursday.

Westar Energy Inc. said CEO William Moore hasn’t decided exactly when he’ll step down in favor of Mark Ruelle, who is now chief financial officer and one of three executive vice presidents. The Topeka-based utility, which has about 687,000 customers, announced the coming changes at its annual shareholders meeting.

Both Moore and Ruelle were among a group of executives who returned to Westar late in 2002 and early 2003, following the resignation of former CEO David Wittig.

After Wittig’s departure, federal prosecutors alleged that Wittig had looted the company, but he’d ultimately see criminal charges against him dropped. Westar abandoned Wittig’s strategy of diversifying the company’s business, opting to resume operating as only an electric service provider.

“Mark was instrumental in Westar’s return to being a strong, successful electric utility,” said board Chairman Charles Chandler IV. “Mark has been integral in developing and executing Westar’s business strategy.”

Chandler also praised Moore for helping to “restore the company and guide it to its sound state.”

Moore had been with Westar and its corporate predecessors for 22 years before leaving in 2000, during Wittig’s tenure as CEO. He returned late in 2002 as an executive vice president and chief operations officer under Wittig’s replacement as CEO, Jim Haines Jr. Moore succeeded Haines in the top job in June 2007.

Ruelle held financial and planning jobs at Westar’s corporate predecessors before leaving in 1997 to become senior vice president and chief financial officer for Las Vegas-based Nevada Power Co. He became the Nevada utility’s president in 2001, then returned to Westar in his current job.

In afternoon trading after Westar’s announcement, the company’s shares were unchanged at $27.61.

When Wittig left Westar, its debt had almost doubled in just seven years, to more than $3 billion. The company had jumped into monitored security services, dropped a natural gas service business and unsuccessfully pursued mergers with two other utilities.

Critics accused Wittig of enriching himself even as his company faltered and its stock price dropped — to as little as $9 a share, something he strongly denied.

State regulators concluded just months before Wittig left that the company was trying to push too much of its debt onto its regulated utility operations — unfairly burdening ratepayers — and ordered a restructuring of the utility’s management.

Wittig resigned facing a federal indictment on fraud and money laundering charges over a loan in an Arizona real estate deal. After a jury convicted him on all counts, he’d be sentenced to two years in prison.

A year after Wittig left Westar, federal prosecutors filed separate criminal charges over his management. A 2004 trial of Wittig and another former Westar executive ended with a hung jury. Convictions from a second trial in 2005 were overturned on appeal, and prosecutors dropped all charges last year before a third trial.