Sept 12 (Reuters) - Ajit Jain, the longtime top

insurance executive at Warren Buffett's Berkshire Hathaway ( BRK/A )

, 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 given for the sale.

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 topped $1 trillion for the first time.

Berkshire has slowed its own stock repurchases and let cash

build to a record $277 billion.

Cathy Seifert, an analyst at CFRA Research 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 ( BRK/A ) 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 and 105 held by the trusts and 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.