Ed Miliband was addressing the Welsh Labour conference in Llandudno Ed Miliband has pledged a Labour government would clear up confusion over what the Welsh assembly can and cannot do.He told the party's Welsh conference in Llandudno Labour would legislate so that powers are assumed to be devolved "unless specifically reserved".
Mr Miliband said it would be "bringing Wales into line with Scotland".
Labour's Welsh government was showing the difference the party can make, but it still faces NHS challenges he said.
It follows sustained criticism of the Welsh NHS's performance by UK Conservative ministers.
The plan to move to reserved powers for Wales was proposed by the UK government-appointed Silk Commission inquiry into devolution.
'Big challenges'Mr Miliband said: "We all remember what happened when Wales tried to keep the agricultural wages board and protect vulnerable farm workers.
"It ended with the ridiculous spectacle of a Conservative secretary of state scuttling to the supreme court to try to stop the Welsh government ensuring fairness in agriculture.
Live stream of Welsh Labour's 2014 spring conference
"Well that is wrong, and under a Labour government it will never, ever happen again."
He said Labour in Wales had "big challenges to meet on the NHS, like better, early diagnosis and support for the older population".
But he added Wales had "half the A&E consultants" and the number of nurses was being "savagely cut back" when the Conservatives were last in charge of the Welsh health service.
Mr Miliband accused David Cameron of being "desperate" to talk about the NHS in Wales because of the "billions wasted" on a "top-down reorganisation" of the NHS in England "that nobody wanted and nobody voted for".
Later, First Minister Carwyn Jones will seek to "set the record straight" on the Welsh NHS, after Tory attacks on it.
He will accuse UK ministers of launching a "Tory war on Wales", putting investment in Wales at risk.
In his speech, Mr Jones will tell the conference: "Far from a Respect Agenda, we now find ourselves on the frontline in the Tory War on Wales.
Rail electrification First Minister Carwyn Jones argues Conservatives are inflicting "collateral damage" on Wales, to win votes in England"Day after day we see attack after attack, on the NHS and those who work in it.
"On our schools, and on our teachers.
"On the Welsh language, on our economy, on devolution - on Wales itself."
Mr Jones will also focus strongly on the continuing row between the UK and Welsh governments over who should pay for electrification of rail lines in the south Wales valleys.
The Welsh government insists UK ministers agreed to bear the cost, totalling hundreds of millions of pounds, but the UK government says a deal was done for the Welsh government to foot the bill.
A senior Labour source told BBC Wales the party is now wondering if a "war of words" is developing into a situation where money from UK ministers for Wales is "drying up".
'Shared values'The first minister is expected to aim the criticism in his speech entirely at the Conservatives.
With May's European elections looming, Mr Jones will issue a rallying call to supporters and activists.
He will say: "Wales has always been proudly European. We have always seen the very real benefits of being a part of a wider European ideal - with shared values and principles.
"Economically we cannot afford to leave and it's time we had a proper debate about the very serious consequences that withdrawal would have on the very fabric of Welsh life."
Labour believes the "constant" attacks on Welsh public services are angering party activists, encouraging them to go canvassing and making the slogan it began using at the 2011 assembly election, "standing up for Wales", highly relevant for this European poll.