The cause was ovarian cancer, her husband, William Jahnke, said. She had been treated for three types of cancer since 2002.

As its chief executive, Ms. Dunn built Barclays Global Investors into the largest institutional money manager in the country; Fortune magazine ranked her among the most powerful women in business. She was later named the nonexecutive chairwoman of Hewlett-Packard after the firing of Carly Fiorina as chief executive and chairwoman in 2005.

While Ms. Dunn was chairwoman of Hewlett-Packard, the company’s board became concerned about leaks of its deliberations to the press. Ms. Dunn authorized a spying operation and put it in the hands of outside investigators, who ran amok. They obtained phone records of board members, employees and journalists who wrote about the company and followed some of them. They even considered an operation to enter the San Francisco offices of The Wall Street Journal posing as a cleaning crew in order to snoop.

Ms. Dunn maintained that she was a scapegoat, saying her actions had been taken with the board’s knowledge and approval.

She later testified before a Congressional subcommittee that she had not directed the investigations but had been guided by the company’s lawyers. Documents submitted to the subcommittee showed that the company’s lawyers had started the operation before informing Ms. Dunn of it, although the efforts were known internally by the name of a Hawaiian resort, Kona. The lawyers told her that the phone records had been obtained legally, she said. She later resigned from the board.

As a result of her role, she was indicted along with four others in California on felony charges of using false pretenses to obtain confidential information from a public utility, unauthorized access of computer data, identity theft and conspiracy.

But the state dropped all charges against Ms. Dunn shortly afterward, saying the action was “in the interests of justice.” She had just learned of a recurrence of cancer. She also battled breast cancer and melanoma.

“She was a really gifted businesswoman from very humble beginnings,” said a friend, Karen Kaplowitz, organizer of the Legal Momentum Aiming High awards, one of many honors Ms. Dunn received. “She rose through the ranks because she was very good at what she did.”

Patricia Cecile Dunn was born on March 27, 1953, in Burbank, Calif., the daughter of a vaudeville actor and a Las Vegas showgirl. Her father died of a heart attack while she was still a girl. The family then moved to Marin County, north of San Francisco. Her mother later died of breast cancer.

Ms. Dunn attended the University of Oregon before transferring to the University of California, Berkeley, where she graduated in 1975 with a degree in journalism. After briefly working for a community newspaper in San Francisco, she was hired as a secretary for Wells Fargo Investment Advisers (which became Barclays Global), then rose through the ranks as she earned a reputation as an ace saleswoman.

She was among the first women to run a large investment management company in the United States, and she introduced an index fund and other computer-intensive quantitative investment management techniques in wide use today.

Her most important accomplishment there was the creation of Exchange-Traded Funds, which despite initial resistance from the firm’s corporate parent became a highly lucrative product. E.T.F.’s are a basket of stocks that reflect the industry category or an index.

Besides Mr. Jahnke, her husband of 30 years and the former chief executive of Wells Fargo Investment Advisers, Ms. Dunn is survived by their two daughters, Janai Brengman and Michelle Cox; a son, Michael Jahnke; a brother, Paul Dunn; a sister, Debbie Lammers; and 10 grandchildren.

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