Seattle ? Even as Apple Inc. acknowledges that all is not well, the extent of Steve Jobs’ health problems remains a closely guarded secret.

The Apple chief executive, a cancer survivor, said Wednesday he is taking medical leave until June, a move that sent the company’s shares plunging 7 percent.

Apple’s chief operating officer, Tim Cook, will take over Jobs’ responsibilities while he is on leave, though Jobs said he plans to remain involved in major strategic decisions.

The announcement marks a reversal from just a week ago, when Jobs, 53, tried to assure investors and employees his recent weight loss was caused by an easily treatable hormone deficiency.

But investors weren’t reassured. Nor do Jobs’ medical issues seem to be quite so simple.