The budget crisis in the Oakland schools has reached a critical level, with the situation so desperate that top-level administrators are voluntarily giving back part of their paychecks, and layoffs as well as classroom cuts are imminent.

The district’s most pressing concern is a $15.1 million deficit in this year’s budget, which will require schools and the central office to slash expenditures even though the academic year is nearly half over.

Without immediate action, and with another $11 million in cuts needed to balance next year’s budget, the district is at risk of a state takeover — again.

“It is not imminent; however, it is serious,” said Alameda County Schools Superintendent Karen Monroe. “Oakland has little margin for error at this point.”

The district is still reeling from a $100 million bailout and state takeover in 2003, with $40 million still owed to California from that crisis.

Yet those charged with preventing a similar fiasco — a state-appointed fiscal trustee, the county superintendent, the school board and district leadership — have failed to stave off crisis.

Despite its checkered economic past, the district has been spending beyond its means again, a multiyear pattern masked in part by accounting tricks and lax oversight, district officials acknowledged. To cover the deficits, the district has dug into its reserve, pushing the rainy-day fund below state-required levels.

“In fact, there have been internal warnings about fiscal issues for several years that were not fully addressed,” district Superintendent Kyla Johnson-Trammell said in an email. “As a result, we have spent beyond our means and depleted savings to the point where immediate action is necessary.”

Johnson-Trammell, appointed superintendent in May, inherited the problem from her predecessor, Antwan Wilson, who left in February to run the Washington, D.C., schools.

The overspending at times has been eye-popping. In 2014, for example, the district budgeted $7.1 million for consulting services, but ultimately spent $22.6 million that year.

Last year, the board budgeted $10.4 million for supervisors and administrators, but spent $22.3 million.

The exception to that trend was in the category of books and supplies. In 2016, the district planned to spend $20.1 million on such materials, but spent only $6.8 million.

District officials and county Superintendent Monroe said several additional factors have contributed to the overspending, including increases in special education costs, big spikes in pension payments and declining enrollment.

But through it all, the district has had lax internal controls, meaning those in charge of the budget failed to monitor spending or flag problems. Last year, for example, the district’s enrollment was 400 students lower than expected, yet Wilson failed to adjust staffing to reflect that — which cost the district more than $3 million in unexpected expenses.

In July, the state assigned a new trustee, Chris Learned, to oversee the Oakland schools. The previous trustee, Carlene Naylor, retired.

Learned, a veteran in school finance who came out of retirement to take the job, pored over the district’s books and came to a quick conclusion: “My thought was, boy, I sure liked retirement,” he said.

The district, he added, “hasn’t been managed well.”

Learned said he is playing an active role in ensuring that the district doesn’t keep making the same mistakes that occurred under Wilson’s tenure.

“I don’t agree with a lot of what I saw him do. I think he was very insistent on getting his way,” Learned said. “The role of the trustee is to be sure that the board and the superintendent are not making decisions that are putting the district in financial risk.”

On Wednesday night, the Oakland school board officially acknowledged the need to balance the budget, approving a plan of action, including an expected vote on Nov. 27 to identify specific ways to slash $15.1 million from this year’s budget. The superintendent vowed to clean up the mess.

“As leader of Oakland Unified School District, I want us to be known as the district that can and does overcome fiscal adversity while meeting the diverse needs of students,” Johnson-Trammell said. “I am committed to putting us on the right path to fiscal stability.”

Yet the expected cuts required to do that prompted afternoon protests on several street corners Wednesday, with teachers and community members lambasting the district’s mismanagement as well as the state’s underfunding of schools.

“Nobody had the gumption to say no to Antwan Wilson,” said Trish Gorham, president of the Oakland Education Association, the local teachers union. “We know there have to be cuts.”

Gorham added, however, that she thought $15 million in cuts was too drastic, especially coming midyear.

Hoping to reduce the deficit, several members of the district’s top leadership last week decided to donate a part of their salaries back to the district, said district spokeswoman Valerie Goode, although specific numbers weren’t available.

At this point, principals and other unionized administrators are not part of that effort, and their participation would have to be established through collective bargaining, Goode said.

But it will take a lot more than salary donations to balance the budget. Learned believes the superintendent and school board are on track to make the decisions necessary to get back into the black — but it will take time to stabilize.

“I think they are getting it, but it’s going to be painful,” he said. “I’m working with them and really believe that Kyla is listening, the board is listening, and there will be changes that will make this district much more efficient, much more transparent and it’s just going to take this fiscal year to get it back in shape.”

Jill Tucker is a San Francisco Chronicle staff writer. Email: jtucker@sfchronicle.com Twitter: @jilltucker