The Principal Financial Group Inc. plans to acquire the mutual fund management business of Washington Mutual Inc. for $740 million.

Principal, Des Moines, Iowa, has agreed to buy WM Advisors Inc. from Washington Mutual, Seattle, for cash. WM Advisors manages the WM Group of Funds and its subsidiaries.

WM Advisors has more than $26 billion in assets under management, including about $21 billion in the WM Funds. The firm provides investment advice for mutual funds, variable trust funds and asset allocation portfolios for about 800,000 fund shareholder accounts.

The transaction would bring managed assets for the insurer’s Principal Mutual Funds division to about $49 billion, from the current total of $28 billion.