The Welsh First Minister Carwyn Jones said he supports a proposal that could see £500bn in borrowing to boost the British economy.
The suggestion has been made previously by the shadow chancellor, John McDonnell, and could become a Labour manifesto pledge for June's election.
On a special BBC Wales' Sunday Politics leaders' debate, Mr Jones said there has never been a better time to borrow.
But Welsh Conservative leader Andrew RT Davies was critical of the proposal.
"In 1945, a Labour government came in after the war when things were much, much worse than they are now, when the UK was in a far more difficult state," said Mr Jones.
"Yet, it created the NHS, it made sure the economy was rebuilt, it built houses. All these things were done at a far more difficult time.
"If they could do it - there is no reason why a Labour government can't do it after June."
'Confidence' to repay
Describing the Conservatives as the "low tax party", its Welsh leader said it was their job to make sure the UK finances "are in good health".
"You can only borrow if people have confidence that you can repay that borrowing," said Mr Davies.
"When you look at Labour's commitment to borrow £500bn - which I might say the first minister has just endorsed - you could suddenly see the financial markets running a mile from the UK."
The Plaid Cymru leader Leanne Wood told the programme that Wales remained "under threat from an extreme Tory Brexit" that risks leaving the single European market and threatens jobs.
"Wales needs a team of MPs with a strong voice defending Wales, and we have an opportunity to provide that in this election," she said.
Asked whether she wanted to be part of that team in Westminster, she reiterated earlier comments on standing for Parliament, stating: "I've got a big decision to make over the next couple of days."
The only Liberal Democrat MP in Wales, Mark Williams, said his party was going to stand-up for the whole of the country - and that Theresa May had made it clear that this election was about Brexit.
The Ceredigion MP said he was delighted to hear his UK leader Tim Farron rule out any future coalition deals with either Labour or the Conservatives.
"Thank goodness for that. I've been waiting for that for a long time... because it's important that people have clear unequivocal choices," said Mr Williams.
The UKIP leader in the Assembly and former Conservative MP Neil Hamilton said the general election was all about "effective opposition".
"The best opposition to the Conservatives is one which forces them to get the best Brexit deal possible for Britain, to deliver on Theresa May's promises on immigration for example," he said.
"We are the guard dogs of the Brexit process."