There must be no half-measures on the reform of social care, campaigners and council chiefs are warning, amid signs ministers are getting cold feet.
Eighty-five groups, including the Local Government Association and leading charities, have made the plea in a letter to David Cameron.
It says that without radical change the elderly and disabled will be left living in "misery and fear".
The letter comes at a critical time in the reform process in England.
A White Paper setting out new plans, including how to fund care in the future, was expected to be published by Easter.
Ministers are now promising it will be released by the summer.
But fears are growing that even if the plans are set out in the coming weeks, they will fall short of the radical reform originally promised.
Behind the scenes officials are already talking about not addressing the trickiest question - paying for care - until the next parliament.
But the letter - published in the Daily Mail - urges the prime minister to show leadership.
It says he should convene a summit before the White Paper to galvanise support.
It says: "Social care is in crisis - the system is chronically under-funded and in urgent need of reform.
"Without this, too many older and disabled people will be left in desperate circumstances: struggling on alone, living in misery and fear."
It goes on to say that "delay or half-measures" will not be tolerated.
And it adds: "We want disabled and older people and their families to be able to live without fear of what tomorrow might bring.
"We are asking you as prime minister to show the vision and courage to make this a reality."
Helena Herklots, the chief executive of Carers UK and one of the signatories of the letter, said the organisations had come together as the next few months presented a "real opportunity" to get reform right.
But she warned without a push from the top of government, the risk was that the "political will" would not be there.