Lancashire County Council will run out of money within three years, a report has warned.
A review into the Labour-led authority's finances predicts its reserves will be gone by April 2019 with a deficit of almost £400m by 2021.
County council leader Jennifer Mein said it means even with planned cuts it was not "currently financially viable".
Tory group leader Geoff Driver branded the multimillion-pound report "a waste of money".
Ms Mein said: "We have got to look at further ways to save money or increase our income.
"We are eating into our reserves now... it won't be long before they are gone."
She added: "We need to be able to increase our income and need the government to recognise the need here in Lancashire is very, very great and possibly more great than other parts of the country."
The Department for Communities and Local Government said: "The government has provided a long-term funding settlement which will give Lancashire County Council £2.9bn to spend between now and 2020.
"This will allow them to deliver high quality services whilst keeping council tax bills down."
Councils have to maintain roads, street lights, empty bins and provide social care for the elderly, vulnerable and children by law.
The government would have to act if these statutory services were axed.
Councillor Geoff Driver, leader of the Conservative party, said: "We objected to the report which cost several millions to tell them something they already knew."
Earlier this month the authority confirmed it was going ahead with the closure of 28 libraries and 31 children's centres as part of £200m of cuts it needs to make by 2020.
It has also increased council tax by 4%.
The report will go before a council cabinet meeting on 6 October.