Many councils are struggling with moves to give individual people their own budgets to spend on social care, a watchdog claims.
The Audit Commission warns some need to make significant efforts to meet targets agreed for England last year.
In particular, people with mental health problems could miss out, it claims.
The Department of Health welcomed the report, urging councils to speed up reform.
"Personal budgets" are designed to give people who use social care, and their carers, more choice and control over how their services are provided.
The money to pay for them can be provided directly to the user in cash, or held and used on their behalf by a council or private care firm.
The policy, launched in 2007, was backed by the coalition government in May this year.
However, the Audit Commission, an independent body which looks at the effectiveness of public bodies in England, says that while some local authorities are on course to meet a target by offering 30% of eligible people their own budget by April 2011, most are not.
Only six of the 152 councils are currently meeting it, the watchdog adds.
What is more, a survey earlier this year showed only 6% of total spending on adult social care had so far been allocated to personal budgets.
The latest report, compiled using national statistics and in-depth analysis of 12 councils, suggests that local authorities face various challenges when introducing personal budgets to the thousands of local people who need them.
Not only do they have to decide exactly how much money to give each "budget-holder", but they have to change their financial systems to cope with the new system, and provide information to people on how to use it, while making sure that there is a local "market" in social care where the budgets can be spent.
Andy McKeon, managing director of health at the Audit Commission, said: "Introducing this radical change in the funding of social care is a challenging, and ongoing process.
"The rationale behind personal budgets is not saving money, but empowering service users. Personal budgets mean personal choice."
Richard Humphrey, from the King's Fund think-tank, said that the response of some councils had been "disappointing".
"Some have achieved dramatic things but the progress in others raises questions - in one council, 60% of eligible people have a budget, while in another, it's just 13%.
"Councils have all signed up to this - now they need strong leadership to get on with the job."
One of the problems highlighted by the watchdog is social care for people with mental health issues.
Providing personal budgets would mean disentangling money not just from local authority funds, but from NHS funds as well.
Many authorities questioned did not provide budgets for these people - with some saying there was a "financial risk" in giving individuals with mental health problems control of their own funding.
Simon Lawton Smith, from the Mental Health Foundation, said that it was not a "good omen" for the future.
However, a spokesman for the Local Government Association, which represents councils, said that the report was "somewhat outdated", with significant progress made since its figures were gathered.
Local authorities remained committed to personal budgets, and a fresh agreement between all the bodies involved in social care would be announced at a conference next week.
A Department of Health spokesman said that the report echoed its own messages to councils.
He said: "This should help those councils that still need to get to grips with their financial systems to pick up the pace of reform."