Funds committed to reforming adult social care in England have been cut by 58%, according to the National Audit Office (NAO).
More than £1bn of the £1.74bn agreed with the Treasury for system reform has been diverted to other care priorities.
The watchdog says the government has "scaled back" its plans and is "behind schedule even on its revised plans".
The government says it remains committed to reform.
The National Audit Office is the UK's independent public spending watchdog, and holds the government to account through its audits.
According to tits report, the Department of Health and Social Care (DHSC) may now only spend £729m on its planned system overhaul until 2025.
In December 2021, the government announced a 10-year vision to improve adult social care, which included a cap of £86,000 on the amount that a person would pay for social care in their lifetime.
It was due to be introduced in October 2023, but in Chancellor Jeremy Hunt's Autumn Statement last year it was postponed by two years, and up to £7.5bn was committed to the sector to help ease immediate pressures.
Other reforms included new supported housing, technology to improve care quality and safety, and investment in training and qualifications.
The NAO says funding was reprioritised "in favour of helping to stabilise the sector" amid rising inflation pressures and concerns about a lack of care places resulting in people getting stuck in hospital.
Liberal Democrat Health and Care Spokesperson Daisy Cooper MP said the "damning" report showed "the chronic neglect of adult social care under this Conservative government".
"The shockingly dismal state of care is putting huge pressure on the NHS while leaving the elderly and vulnerable to suffer," she said.
"The Liberal Democrats would tackle staff shortages by paying care workers properly, bring in free personal care and increase the Carer's Allowance for unpaid carers."
Despite some recent signs of improvement, the care system remains under significant pressure.
Among the many challenges are high waiting lists, which local authorities reported had increased by 37% between November 2021 and April 2022.
Job vacancies in adult social care in England have increased by 173% in the past decade and, despite a recent fall, stand at around 152,000.
The NAO report also found the government has not established an "overarching programme to coordinate its reforms, making it difficult to know if it is on track to achieve its objectives".
It said the DHSC does not have a long-term funded plan for transforming adult social care, and is delivering on two of its eight workforce projects - supporting international recruitment and adult social care volunteering - but the other six are in development.
"The department's Next Steps paper, published in April 2023 - which contained high-level plans for system reform - does not go beyond the current spending review period," the NAO said.
Gareth Davies, head of the NAO, said the government must demonstrate how it is delivering on its plans.
"To maximise its chances of succeeding, government will need to ensure it understands the impact of its ambitions on local authorities and other stakeholders, and establish a costed plan which ensures delivery of its long-term goals," he said.
A DHSC spokesperson said it remained committed to reform and was investing up to £700m this year and next to make major improvements to the adult social care system.
This includes £42.6m to support innovation in care and an increase to the Disabled Facilities Grant of £50m.
"Additionally, we have made up to £8.1bn available to help local authorities tackle waiting lists, low fee rates, and workforce pressures, £570m of which will help local authorities improve adult social care provision, in particular by boosting the workforce," the spokesperson added.