The unfunded liability climbed 13 percent to $64.5 billion as of June 30, according to a report from actuaries released Monday. The system had about 69 percent of assets needed to cover promises to current and future retirees at the end of fiscal 2011, down from about 71 percent a year earlier.

The widening gap may require increased state funding, plan officials have said. Public pensions nationwide had a median of about 75 percent of the funds needed to cover obligations in 2010, according to Bloomberg Rankings data. The California fund’s overseers said losses on invested assets in 2008 and 2009 added $12.7 billion to the new deficit figure.

“The projected revenue shortfall is due primarily to investment return experience averaging 5.5 percent per year over the last decade that was significantly less than the long-term actuarial assumption of 7.5 percent,” Milliman Inc. consultants said, according to the report. The study will be formally presented to the $152 billion plan’s board members April 12.

Smoothed Results

The so-called funding ratio has been less than 100 percent since 2001. Because the ratio is “smoothed” by averaging three years of investment returns to minimize volatility, the latest gap only partially reflects the almost 24 percent net gain from investments in fiscal 2011, according to the report. The system earned 2.3 percent on assets in the past calendar year, according to a January study.

Teachers pay 8 percent of their income toward retirement. Districts add 8.25 percent, while the state’s share is about 2 percent. Contribution rates for teachers and school districts haven’t changed since 1990.

In February, plan overseers lowered the assumed rate of return on investments to 7.5 percent from 7.75 percent. The change retroactively added $3.5 billion to the system’s funding gap as of June, according to the plan report.

By comparison, the California Public Employees’ Retirement System, the largest U.S. public pension, with $234.8 billion of assets, has between 70 percent and 75 percent of the money it needs to cover future liabilities, according to Brad Pacheco, a spokesman. Calpers, as the fund is also known, cut its assumed rate of return to 7.5 percent from 7.75 percent March 14.

The system for state and local government workers was fully funded when the last recession began. Its ratio of assets to projected costs dropped to as low as 65 percent after a 28 percent drop in value from December 2007, when the slump started, to June 2009, when it ended, as the global downturn depressed equity and property values.

In fiscal 2011, Calpers had an almost 21 percent return on investments, its best performance in 14 years.