UnitedHealth Group Inc. says the cost of correcting accounting for past stock compensation programs may be much higher than it originally had predicted.

UnitedHealth, Minnetonka, Minn., a large managed care company, has been reviewing the results of a compensation program study commissioned by its board.

“Although the company is not yet able to determine the final amount of the non-cash compensation charges and additional cash charges resulting from potential tax liabilities, the company anticipates that it will be significantly greater than the estimate contained in its Form 10-Q for the quarter ended March 31, 2006,” UnitedHealth says in announcement released today.

Back in March, UnitedHealth suggested that it might have to take a charge of about $286 million.

“The company has concluded that, due solely to the stock option matter, its financial statements and similar communications for the years ended 1994 to 2005 and the interim quarters through Sept. 30, 2006, should no longer be relied upon, and the company will delay filing its Form 10-Q for third quarter 2006,” UnitedHealth says.

In addition, UnitedHealth has “substantially remediated a material weakness in its internal controls relating to stock option plan administration that it has now concluded existed as of Dec. 31, 2005,” the company says.

In other news, the UnitedHealth board has:

- Negotiated a 4-year employment agreement with Stephen Hemsley, the company’s president.

- Elected G. Mike Mikan, who has been the company’s senior vice president of finance, to the position of chief financial officer. Mikan succeeds Patrick Erlandson, who has resigned as CFO and “will be assuming operational duties within the company,” UnitedHealth says.

- Named Forrest Burke, the general counsel for the company’s UnitedHealthcare unit, to be acting general counsel for the parent company while the company searches for a permanent general counsel. Forrest Burke is not related to UnitedHealth Chairman Richard Burke, the company says.

- “Received voluntary written agreements from senior company executives, to ensure that there is no potential for financial gain from the misdating of any option, by resetting the exercise prices of all applicable exercised and unexercised options with recorded grant dates between 1994 and 2002,” UnitedHealth says.

- Hired search firms to help it find new directors and fill several executive positions.