Organisations that rely on EU funding “deserve certainty” from Westminster, the Welsh Government has said.
Welsh ministers are publishing proposals for how they think grants should be awarded after the Brexit transition period ends on 31 December.
The UK government said details of its shared prosperity fund would be set out after the spending review next week.
The Conservatives said the Welsh Government had failed to deliver change needed using EU funding.
But the Welsh EU transition minister Jeremy Miles said the UK government should have made an announcement “months ago”.
He said the Welsh Government had “learned lessons” from the way it has spent billions of pounds in EU funding since 2000.
Much of the money has gone to the West Wales and the Valleys region which, as one of the EU’s least prosperous areas, has qualified for the top level of funding three times since 2000.
Research by the House of Commons says it would probably have qualified again were Britain staying in the EU.
Mr Miles denied money had been wasted, saying it had created jobs and helped train thousands of people.
He said the UK government had to deliver on promises to match EU funding and respect the devolution settlement.
“But what is obviously the case is that with less than 50 days to go to the end of the transition period, organisations, projects right across Wales deserve certainty of knowing whether the replacement programmes are capable of supporting what they’re doing,” he said.
Ministers in Cardiff have accused the Conservatives at Westminster of mounting a post-Brexit power grab.
Legislation going through Parliament would give the UK government new powers to spend in devolved areas otherwise under the control of Welsh ministers.
It said the powers would “drive our economic recovery from Covid-19 and support businesses and communities right across the UK”.
Running for the Conservative leadership in 2019, Boris Johnson said he wanted to see “a strong Conservative influence” over how funding was spent.
A spokesman for the UK government said the replacement fund would tackle “inequality and deprivation across all four nations” of the UK.
“We will continue to work closely with the devolved administration in Wales and other interested parties as we develop the fund. Further details will be set out following the upcoming spending review,” he said.
Darren Millar, of the Welsh Conservatives, said Brexit was a chance to “reboot and revamp” regional funding around Wales.
“The new UK shared prosperity fund will replace the overly bureaucratic EU system and Wales is guaranteed to receive at least the same level of funding as we currently receive from the EU,” he said.
“This funding will be used to tackle inequality and deprivation right across Wales but local decision-making on how it is spent, not a ‘Welsh Government knows best’ and Cardiff-centric approach, will be critical to its success.”