The coronavirus pandemic has blown a multibillion-dollar hole in California’s budget, one that is likely to force Gov. Gavin Newsom and lawmakers to make difficult decisions in the years to come.

The shortfall is likely to total roughly $35 billion in 2020-21 alone, the nonpartisan state legislative analyst told senators who convened a special budget hearing on the coronavirus Thursday in Sacramento. The shortfall could snowball by an additional $85 billion in the years that follow, Legislative Analyst Gabriel Petek said.

“If budget problems of this magnitude were to emerge, they would exceed the state’s reserves,” Petek said, in something of an understatement.

The surplus that the Legislature, Newsom and former Gov. Jerry Brown accumulated over the past decade totals about $21 billion, about $4 billion of which will probably be needed this year to meet the constitutional requirement of a balanced state budget.

Petek’s estimate, which he presented via videoconference to two senators wearing masks in a Capitol hearing room and several others who tuned in remotely, renders all but moot Newsom’s January budget proposal. The governor had asked for new spending to add homeless services, wildfire prevention programs and health care for undocumented immigrant seniors.

Petek said it will realistically “probably take several months” for the state to have a clear picture of its budget situation given the sudden nature of the coronavirus pandemic, which has halted most economic activity and will certainly cause a sharp drop in tax revenue.

He suggested lawmakers pass a “baseline budget” that doesn’t add nonmandatory expenses and assumes the state continues existing service levels.

“Doing that may make it easier to address whatever budget problem does emerge this summer,” Petek said.

The hearing gave the senators a look at what will dominate their time when they return from their emergency recess, which began last month and is now scheduled to end May 4. Newsom must release a revised spending plan by next month, and by law the Legislature has to pass a balanced budget by June 15 or go without pay.

State Sen. Holly Mitchell, a Los Angeles Democrat who leads the budget subcommittee that met Thursday, said that while the situation is grave, California is “much better” prepared than it was before the last economic collapse in 2008.

Then, the state had little budget reserve, Mitchell noted. The current cushion will at least enable California to avoid borrowing immediately, gutting programs, and issuing IOUs instead of paychecks to state workers, she said.

Mitchell said the level of aid California receives from the federal government will be key in shaping the speed of its recovery. One issue Congress is wrestling with in its next coronavirus relief bill is how much money to give to state and local governments.

“We know that most of the work is still ahead of us,” Mitchell said. “We understand the gravity of the situation.”

Dustin Gardiner is a San Francisco Chronicle staff writer. Email: dustin.gardiner@sfchronicle.com Twitter: @dustingardiner