By Jonathan Stempel

(Reuters) -Ajit Jain, the longtime top insurance executive at Warren Buffett's Berkshire Hathaway, sold more than half of his Class A shares in the conglomerate this week.

According to a Wednesday night regulatory filing, the 73-year-old Jain sold 200 Berkshire Class A shares on Sept. 9 for about $139.1 million, at an average price of $695,418 per share.

The sale included 104 shares Jain held directly and 96 held by family trusts. No reason was provided.

Berkshire did not immediately respond on Thursday to a request for comment.

Jain's selling occurred five days after Berkshire's share price peaked above $727,000, and less than two weeks after its market valuation first topped $1 trillion.

Berkshire has slowed its own stock repurchases and let cash grow to $277 billion, perhaps in part reflecting stock valuations.

Cathy Seifert, a CFRA Research analyst who rates Berkshire a "buy," said Jain's selling may reflect personal circumstances rather than his view of Berkshire's prospects.

"Those of us who have watched Berkshire Hathaway for a long time have suspected there may be a changing of the guard in insurance operations," she said. "My sense is that he may be moving on, and I suspect that is behind his stock sales."

Jain still oversees 166 Class A shares, including 61 held directly, 55 held by the trusts, and 50 held by his nonprofit Jain Foundation.

He also oversees 124,308 Berkshire Class B shares, equal to about 83 Class A shares, held by the foundation.

Born in India, Jain joined Omaha, Nebraska-based Berkshire in 1986 and led its expansion in reinsurance, with a specialty in pricing for large risks such as natural catastrophes.

Buffett has credited Jain with adding tens of billions of dollars of shareholder value, and once said that if he, Jain, and late vice chairman Charlie Munger were in a sinking boat and only one could be saved, "Swim to Ajit."

Greg Abel, 62, Berkshire's other vice chairman, is expected to eventually succeed Buffett, 94, as chief executive.

He owns about $150 million Berkshire Class A shares, compared with $78 million owned by Jain directly or in the trusts. The shares closed down 0.7% at $675,380 on Thursday.

"We continue to be comfortable that the interests of Mr. Jain and Mr. Abel are aligned with shareholders," Edward Jones analyst James Shanahan said in an email.

(Reporting by Jonathan Stempel in New York; Editing by Leslie Adler and Marguerita Choy)