Carwyn Jones and Peter Hain enjoy a joke by Rhodri Morgan [R]
Welsh Labour's new leader says it would be difficult to have a "constructive relationship" with a future Tory UK government which cut public services.
Carwyn Jones said while a Labour-led assembly government would work with a Conservative administration, it would try to "protect the people of Wales".
He was speaking at an election planning meeting days after winning his job.
But Monmouth Tory MP David Davies said Wales had no reason to fear cuts if it went no further towards "independence".
Rhodri Morgan, who will also be succeeded by Mr Jones as first minister next week, was among those at the Labour meeting in Newport, along with Welsh Secretary Peter Hain. Its aim was to help Labour activists from across Wales prepare for an expected general election in spring next year.
In his acceptance speech after winning the leadership last Tuesday, Mr Jones said Labour's fightback was beginning with the campaign for the Westminster election.
The theme of the day was what Wales would be like under the Conservatives, but Mr Jones said he believed that Labour would win again.
He argued that his party was catching the Tories in the polls, that voters were realising the effect of likely Conservative cuts, and that John Major had also confounded the odds to win in 1992.
Asked about the impact of a Tory win on Wales, he said: "I don't think a Conservative government would hold Wales' best interests at heart. I know that a Labour government in Westminster would.
"So it would be very difficult indeed for us of course as an assembly government if we were put in a position by the Tories where we would have budget cuts that would mean fewer and worse services potentially for the people of Wales.
"But we will do all we can if we are faced by that scenario to protect the people from Wales from all that the Tories would do."
He said Labour would "work with whoever we find in front of us".
However, he said "there needs to be goodwill on both sides, and it's very difficult to see where that goodwill would come from if we were faced with the scenario - and it is a big if - of a Conservative government that wanted to make cuts to public services.
"That would make it very difficult for there to be a constructive relationship. But certainly of course we will look to engage in a businesslike way with whoever is across the table from us."
Conservative MP David Davies said that under Labour the economy was "in pieces," its "ethical foreign policy" had resulted in Iraq, and law and order was breaking down in cities across England and Wales.
Mr Davies said he did not accept that Wales would lose under a Tory government.
"We stuck with the Barnett formula throughout the 18 years of Conservative government between 1979 to 97, and the Conservative government committed to ensuring a needs-based formula to allocate money across the whole of the United Kingdom.
"Providing of course that Wales remains a part of the United Kingdom. And it's Labour that gave us devolution and then the new Government of Wales Act without a referendum and they are now talking about trying to give the Welsh assembly even further powers through some sort of referendum, which I suspect will be heavily rigged.
"The more powers Wales develops and the closer to independence it gets the harder it will be justify large amounts of English taxpayers' money being given to the Welsh assembly.
"There are obviously going to be public spending cuts throughout every area of the public sector.
"That's going to happen whether we have a Labour or Conservative government.
"There's no point in shying away from that because we are borrowing at a rate of £200bn a year and we are not going to be able to get the money for much longer.
"But there's no reason to fear specific cuts in Wales providing of course we don't go any further down the route to independence."