BART, devastated by losses of up to $5 million a week in the wake of the coronavirus pandemic, is desperately seeking money from state, federal and local governments, The Chronicle has learned.

Officials laid out their predicament in letters to House Speaker Nancy Pelosi, U.S. senators Dianne Feinstein and Kamala Harris, state Assemblyman Jim Frazier, state Sen. Jim Beall and Metropolitan Transportation Commission Chairman Scott Haggerty.

BART Board President Lateefah Simon asked for an immediate operating subsidy from the commission, emergency funding from the state and federal money from Congress.

“The reality of BART’s lauded 60% fare box recovery ratio, one of the highest in the country, is we are particularly vulnerable to the loss of fare revenue during catastrophic events like the COVID-19 pandemic, leaving the agency short of critical funding to maintain service,” Simon wrote.

President Trump recently signed the Coronavirus Preparedness and Response Supplemental Appropriations Act, which provides $8.3 billion for pandemic response efforts, setting aside $950 million for states and local agencies, the letters to Harris, Feinstein and Pelosi note.

BART “needs to receive federal funding to help reduce the spread of the virus and to maintain our service levels,” the letters said, noting the rail system’s significance as an engine of the Bay Area economy. Under normal circumstances, it carries 404,000 people each weekday.

Daily revenues slid dramatically for the rail agency as Bay Area employers encouraged or mandated remote work, schools and universities stopped classes, cities barred large events and businesses canceled conferences and conventions. On Monday, BART carried 25% fewer riders than it did during an average weekday in February. On Tuesday, ridership plummeted to 30% and on Wednesday it dropped 35%.

By Thursday, the number of riders had dropped by 45% — to about 222,000 riders — a deep plunge from BART’s normal weekday haul.

That translated into financial losses of between $450,000 and $890,000 a day, or $2.5 million to $5 million a week, the letters said.

Managers at the rail system contemplated cuts to reduce their operating expenses, but found that most expenses come from labor. BART is bound to its labor contracts, and its top officials have also committed to running 10-car trains on a full schedule with increased cleanings during the pandemic. The cost of extra cleanings, hand sanitizer and other protection measures during the crisis has added to BART’s financial woes.

“As we continue regular service levels and increase cleaning to help reduce the spread of the virus, BART has limited options to reduce operating expenses in the short term,” the letters said.

General Manager Bob Powers described the situation in stark terms during an interview Thursday.

“We could be seeing losses of about half a million dollars a day,” he said. “Our fare box is so critical to our budget — we’re very fragilely balanced. A drop in ridership really impacts our bottom line.”

The rail system is far from alone, said Randy Rentschler, legislative director of the Metropolitan Transportation Commission. He and his colleagues have held conversations this week with several major transit operators in the Bay Area, including Caltrain, AC Transit and Golden Gate Transit. All of them are experiencing steep drops in ridership and revenue, Rentschler said.

The MTC has provided financial aid for transit systems during past crises, including the recession of 2009. That economic downturn led to a sharp decline in sales tax revenues, a critical funding source for transit. Fearing that Bay Area transportation could deteriorate without an infusion of cash, the MTC diverted money capital projects to help the agencies.

“So, the MTC has done this before under similar circumstances,” Rentschler said. “We’re evaluating it now.”

He and others worry that the coronavirus pandemic and stock market crash could presage another downturn, which would deepen the financial problems for transit.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan