DALLAS (AP) _ Herb Kelleher, the flamboyant, chain-smoking leader of low-cost carrier Southwest Airlines, has prostate cancer, the company disclosed today.

Kelleher, 68, the co-founder and longtime chief executive and chairman, will begin eight weeks of radiation treatment today at M.D. Anderson Cancer Center in Houston.

The cancer was discovered at an early stage during a routine annual prostate examination, and is in a mild stage of development, said Dr. Andrew C. von Eschenbach, director of the prostate cancer program at M.D. Anderson.

He said Kelleher is expected ``to lead a fully active and productive life just as if he had never had prostate cancer.''

Kelleher co-founded Southwest Airlines in 1971. He was named chairman in 1978 and assumed titles of president and CEO in 1981. His flamboyant leadership and high-flying spirit have been considered the keys to Southwest's success.

The company's disclosure comes just months after a shareholder raised concerns about Kelleher's longevity, complaining about his penchant for cigarettes, Wild Turkey liquor and frequently flying aboard an airline that routinely offers fat- and salt-laden peanuts.

A proposal put forward by the shareholder would have made Kelleher, who is also president, choose between running either the board or day-to-day operations. The proposal never made it for a vote at the company's annual meeting in May.

In the company's statement, Kelleher vowed to commute to Houston for his daily treatments and to be in his Dallas office every morning and early afternoon.

``It would be my guess that our officer group is probably somewhat disappointed that I will be in my office more than normal during the treatment period, since ordinarily I travel several days per week,'' he said.

Kelleher has always had a tongue-in-cheek style that has created a casual corporate culture at an airline known for high customer satisfaction. Fortune magazine named it the country's most admired airline, and this year, the best place to work in the U.S.

As for his personal habits, Kelleher has said he doesn't smoke too much and pointed out that he gives up drinking every February.

Dallas-based Southwest is the nation's fourth-largest carrier in terms of customer boardings. It operates more than 2,450 flights a day and has more than 28,000 employees.

On the news, its stock dipped 12 1/2 cents to $16.37 1/2 a share in late morning trading on the New York Stock Exchange.