Spending at the University of California’s Oakland headquarters has nearly doubled in recent years, and official staff counts vary by nearly 500 people, depending on who’s doing the counting.

So on Wednesday, state lawmakers authorized an audit of UC’s Office of the President to determine whether its $686 million annual budget — more than twice that of the Legislature — is money well spent.

The eight-month, $418,000 audit comes at the request of two influential assemblymen, Phil Ting, D-San Francisco, chairman of the budget committee, and Kevin McCarty, D-Sacramento, chairman of the budget subcommittee on education finance.

“As UC advocates for more state funding, and as it contemplates potential student tuition increases in the future, the Legislature needs a clearer picture of UC costs,” the lawmakers wrote to the chairman of the Joint Legislative Audit Committee, Assemblyman Freddie Rodriguez, D-Pomona (Los Angeles County), to ask the panel to conduct an audit.

UC’s regents are expected to raise tuition for fall 2017 for the first time since 2011. Based on that and a March audit revealing that UC admits thousands of higher-paying out-of-state students with lower grades and test scores than state residents as a way to raise cash, Ting said he wants to know how UC can become more efficient and enroll more Californians.

McCarty told the committee, “We don’t know where all the money is going.”

UC officials countered that they’ve been overwhelmed with six state audits in three years.

“This audit appears to cover much of the same ground as other audits,” said Steve Juarez, UC’s governmental relations director. He suggested a less formal process in which UC would give lawmakers all the information they wanted.

The budget for UC’s Office of the President amounts to about 2 percent of the university system’s entire $29 billion operation — about $3 billion of which comes from state funds.

Slightly more than half the president’s budget, $372 million, pays for programs across UC campuses, laboratories and hospitals. It funds millions of digital books, thousands of students studying abroad, hundreds of agricultural advisers and specialists, HIV/AIDS and breast cancer research, and more, documents show.

The remaining $314 million of the president’s budget pays for UC headquarters and administrative services. This includes running the pension plan and investments, employee benefits, insurance and legal services, among other items.

In July, the UC regents raised the president’s budget by more than $34 million to pay for nonunion employee raises, a pilot program for centralizing campus payroll and human resources operations, and a new cybersecurity system costing nearly $10 million.

But an effort to explain such expenditures by Kieran Flaherty, UC’s deputy to the chief financial officer, was not enough to put the committee’s concerns to rest.

“The Office of the President has a significant number of employees — 1,300? 1,600? 1,200?” said the audit committee’s vice chairman, Sen. Richard Roth, D-Riverside. “The data varies depending on what you’re looking at.”

Juarez said the number of employees was less now than it was in 2009, when there were more than 2,000 people working in the president’s office.

Ting said UC’s website says the current figure is 1,672 full-time employees or their equivalent in part-timers, while the state Department of Finance reports that UC gave it a figure of 1,186 — 486 fewer people.

Elaine Howell, the state auditor, said the audit will identify the true number and cost of employees at the president’s office for the last five years. The audit will also look at the president’s budget and whether campuses benefit from spending by the president’s office, among other areas.

Nanette Asimov is a San Francisco Chronicle staff writer. Email: nasimov@sfchronicle.com Twitter: @NanetteAsimov