Powys County Council is facing a budget crisis after members rejected plans for £12m cuts and a 9.5% council tax hike.
Cuts to libraries, blue badge parking and leisure services were attacked during a stormy seven-hour meeting.
The ruling Independent/Conservative coalition defended its plans to spend more on key services such as schools.
But Labour's Matthew Dorrance called the budget "broken", while Lib Dem group leader James Gibson-Watt urged cross-party talks to settle the row.
"It's quite clear that the cabinet budget does not enjoy the confidence of council," he said.
"We need to consider very carefully on how to proceed."
Aled Davies, the cabinet member responsible for finance, had made one last bid for support, pointing to positive measures such as extra spending on schools, according to the Local Democracy Reporting Service.
"We are doing a huge amount every day that's not always seen," he said.
"Of course we have to respond to the challenges, it's a difficult budget.
"We have probably the most important vote of the year, we must provide a balanced budget and this is a balanced budget."
Eight out of 24 senior management jobs at the authority are being axed with the aim of saving £1.3m a year and to improve leadership.
Government inspectors have told Powys that more still needs to be done to improve children's services after a damning report in 2017 said failings had put youngsters at risk.
Acting chief executive Mohammed Mehmet - on his last day in the post - urged councillors to settle what he called a "robust" budget which protected the council's priorities.
However, audit committee chairman John Morris claimed councillors had not been given all the information they needed to scrutinise a "high-risk" budget.
The budget was voted down by 32 votes to 31, with two abstentions.
The council will look again at settling the budget and council tax on 7 March.