A Labour victory in May's assembly election is Wales' "first line of defence" against the UK government, says shadow Welsh Secretary Peter Hain.
He told the Welsh Labour conference in Llandudno it was an opportunity to "send a message" to the UK coalition.
Mr Hain said Labour had bounced back after the general election, but he warned against complacency.
Referring to Labour's coalition partner Plaid Cymru he called for a majority to "kick nationalists out of government".
He said Wales needed a Labour-led assembly "that will stand up against the Tory-led government's plans to cut vital services".
Savings had to be found in public spending, "but the cuts ordered in Whitehall go too far, too fast", he said.
"Labour is Wales' first line of defence against the broken promises of the Conservatives and their Liberal Democrat allies on VAT, tuition fees and protecting frontline services," he said.
"Vote Labour in May to send David Cameron and Nick Clegg a message."
He hailed the by-election victory in Oldham East and Saddleworth and a "surge up the opinion polls" as signs that Labour had "bounced right back" from the general election under Ed Miliband's leadership.
'A good platform'
"But no complacency," he said. "We have to work very hard to rebuild trust and turn that support from angry protest at the government to solid backing for Labour".
The Neath MP and former Welsh secretary added: "And after all the fantastic Labour by-election victories we have a good platform to win outright in Wales and kick the nationalists out of government."
Labour was reforming its policy-making process "so that party members have a proper say again," he said.
He said UK government plans to cut the number of MPs, which would see Wales lose a quarter of its seats, were "blatantly unfair to Wales".
Plaid Cymru MP Jonathan Edwards reacted to Mr Hain's comments on his party by saying: "Mr Hain must feels extremely threatened by Plaid success in government since 2007.
"It's no secret that some of the more tribal figures within Labour didn't want their party to go in to government with Plaid in 2007 for narrow political reasons and he seems to be increasingly losing touch with reality in Wales as each day passes."
In his speech to the conference on Saturday, First Minister Carwyn Jones said "delivery will be the watchword" of Labour if it wins power in a fourth assembly term.
The Conservatives said the pledge was an admission of failure.
The Tory leader in Cardiff Bay, Nick Bourne, said: "We agree with the first minister that all too often his assembly government has seemed like a 'strategy factory' producing endless paperwork for schools, businesses and the NHS and has fallen short on delivery of improvements to public services."