“This is a really good company with some serious problems,” said Ali Dibadj, an analyst at Sanford C. Bernstein & Co. in New York. He has recommended P&G consider a breakup if earnings don't improve this year. “A lot of those problems have been driven by management.”

Directors don't see a clear internal candidate to replace McDonald, one person said. A.G. Lafley preceded McDonald as CEO, while other former executives include Paul Polman, the CEO of Unilever, who ran P&G's European business until 2006.

Paul Fox, a spokesman for P&G, declined to comment. McNerney, who is also the CEO of Boeing Co., wasn't available for comment through his spokesman.

P&G, the maker of Tide laundry detergent and Duracell batteries, most recently cut its profit forecast last month, citing currency fluctuations and rising commodity costs, even as competitors reaffirmed their projections. In February, McDonald announced a $10 billion cost-reduction plan that included 5,700 job cuts.

'Smidgen Premature'

“If he has lost the confidence of the board, I'm sure they are going to make a change,” Janna Sampson, who helps manage about $2.9 billion, including P&G shares, at OakBrook Investments in Lisle, Illinois, said by telephone. “But it does seem a smidgen premature. I'm not sure the problems are of the CEO's making. He started in a tough economy, and it's not gotten much better.”

In response to Ackman buying a stake, P&G said that it welcomes investment in the company.

“We are focused on creating shareholder value by executing on our plan to deliver top- and bottom-line growth through our $10 billion cost savings program, renewing our focus on innovation, pricing initiatives and improved execution, and reallocating resources to invest in the highest return opportunities,” P&G's Fox said in an e-mailed statement.

Ackman, who has lobbied for shakeups at companies including Target Corp. and Canadian Pacific Railway Ltd., said in an e-mail that the P&G stake purchase is his largest initial investment ever.

The activist investor this year won an effort to remove Canadian Pacific CEO Fred Green and replace him with Hunter Harrison. Ackman also pushed Fortune Brands Inc. to break up, and the company last year split into spirits maker Beam Inc. and a company that sells home products such as faucets and locks. More than two years ago, he led a failed effort to get Target to sell its card unit and divest its land holdings into a real-estate investment trust.

P&G's other shareholders include Berkshire Hathaway Inc., led by billionaire Warren Buffett. The firm held a stake of about 73.3 million shares, or 2.7 percent, as of March 31, according to data compiled by Bloomberg. That's down from 76.8 million at the end of 2011.

McDonald took over P&G's top job in July 2009 after serving as chief operating officer. A West Point graduate, McDonald rose to lead the company's Northeast Asia operations in 1999 after stints in the Philippines and Japan. In 2001, he became president of the global fabric and home-care business. Three years later, he was made vice chairman for global operations.

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