Bosses at Birmingham City Council say £600m of savings must be made by 2017, with £120m in the next financial year.
Cuts of £62m to the Labour-run authority's 2012-13 budget were voted for in February with warnings that 1,100 jobs could go.
Council leader Sir Albert Bore said the authority was still looking at those job losses "over the next few years".
He said some of the council's services would have to be "decommissioned" completely to meet the savings targets.
The council leader warned the authority could face an additional £60m to £70m of savings on top of the £120m for 2013-14, depending on cuts to direct government grants.
He said he had written to Eric Pickles, the minister in charge of local government, for clarification.
Sir Albert said the authority was now looking at cutting £600m in total over the six years running up to March 2017 - £200m more than initially thought.
He blamed successive cuts in government grants for the council's "horrendous" financial situation, which he said had not taken into account population changes, inflation and other costs.
The leader said the government had banned authorities from raising council tax by more than 1.6% without holding a referendum among voters about whether they would be prepared to pay more. He refused to rule that out as a possibility.
Sir Albert said: "This is the end of local government as we have known it.
"But this is not the end of local government completely.
"It needs to be inventive, it needs to find new ways to work with partners like public agencies, schools and the business community to find different ways to do this."
Labour took over the running of the council, the UK's largest local authority, in May from a Conservative/Liberal Democrat coalition.
The council said it would be holding several public meetings from next month over which services should go.
Sir Albert said that at its height, the council employed 19,000 full-time members of staff but that figure would fall to less than 15,000 over the "next few years".
He said it would be mid to late-November before they would have more details on how many and what sort of jobs would be affected, although he said some senior posts could be axed.
Sir Albert said there could be "no more 'salami-slicing' of services".
He added: "With the extent of the cuts over the past few years and with more to come, we have to start decomissioning services.
"I am not looking forward to this but it has to be done."