Welsh police forces would be £25m a year better off if the service was devolved, a Plaid Cymru MP has claimed.
Liz Saville Roberts challenged Theresa May at Prime Minister's Questions, saying Wales had lost 750 officers since the Tories took power in 2010.
Mrs May said crime was at a record low, and that the Conservatives had protected police funding since 2015.
She also pointed to the creation of the National Crime Agency and a national cyber crime unit as boosting resources.
Ms Saville Roberts, who leads Plaid Cymru at Westminster, told the House of Commons: "Police officer numbers in Wales have dropped by 10 per cent since her party came to power."
Referring to figures provided by Dyfed-Powys Police, she added: "If policing were devolved - as it is in Northern Ireland and Scotland - Welsh forces would have extra funding worth £25m at their disposal.
"This would more than replace those lost officers.
"What justification is there for refusing to devolve policing?"
Plaid Cymru said the Dyfed-Powys figures were based on the Barnett formula, which determines public funding for the different UK nations taking population into account, rather than the UK government's separate police funding formula.
The party claimed that changes to the police funding formula would deliver a further £32m cut to Welsh forces.
Responding to Ms Saville Roberts, the prime minister said: "We are currently protecting police budgets. We have been doing that since 2015."
She added: "We're not just protecting those police budgets, we are ensuring that the police have the capabilities they need to deal with new types of crime, creating the national Cyber Crime Unit, creating the National Crime Agency.
"These are all important steps to ensure the police can do their job of cutting crime, and crime is at a record low."