California Public Employees’ Retirement System said Tuesday that Patricia Clarey, a Health Net Inc. executive and former chief of staff for Gov. Arnold Schwarzenegger, has joined its board.

Clarey, a senior vice president and chief regulatory officer for Woodland Hills-based insurer Health Net, joins the CalPERS board as the nation’s largest public pension fund after a significant drop in the value of its stock portfolio due to the real estate market. At the end of 2008, the overall value of the fund had fallen more than 28 percent to $186 billion compared with its peak in October, 2007.

The 13-member board oversees the policies of the system, which also is the nation’s second-largest government buyer of health benefits. Health Net has no Calpers contracts, according to the fund.

Clarey has more than 25 years of public and private sector experience. She served as Schwarzenegger’s chief of staff from 2003 through 2005. She has also directed federal, state, and local government affairs at Chevron Corp. and Transamerica, and served as president of the Transamerica Foundation in San Francisco.

“Pat brings extensive experience in policy issues of importance to CalPERS,” said board President Rob Feckner in a statement.

A Health Net spokeswoman said Clarey’s duties at the company will not change due to her new appointment. Clarey will be the board’s designated representative of the California State Personnel Board, on which she also serves.