First Minister Rhodri Morgan has warned that voter apathy could see a Tory-led "nightmare alliance" running Wales.
Mr Morgan said there was a danger in a "naturally anti-Tory country like Wales" of assuming that Conservatives could never be in government.
He told Welsh Labour's conference that Plaid Cymru and Liberal Democrats could join a "Tory-led triple alliance" after May's assembly elections.
Welsh Tory leader Nick Bourne accused Mr Morgan of lacking ideas and vision.
Mr Morgan, who wants the elections to be about Welsh issues and Labour achievements in Wales, has warned that "noises off" in Westminster - including the "cash for honours" row - could damage the party's chances.
Labour is a minority government in the assembly, and holds 29 of the 60 seats.
In his closing address to the conference in Llandudno, Mr Morgan urged delegates to ensure Labour supporters voted on 3 May, rather than assuming that Labour would win.
The first minister said: "What none of us want to see is Labour defeated in the election, not because the people of Wales wanted to put a non-Labour administration in charge of our country but because we couldn't galvanise our voters into turning out.
"What we don't want to see is thousands of people who forgot to vote on Thursday beseeching Labour on Friday to try and carry on after losing the election.
"'We didn't get round to voting on Thursday because we were sure that everyone else in our street would remember to vote and we're all Labour around here anyway.
Rhodri Morgan and his Cabinet will emphasise distinctive Welsh policies
"But unfortunately democracy doesn't work by hand-wringing on Friday. It works by voting on Thursday and by foot slogging and door-knocking in March and April."
He concentrated his fire on the Conservatives. After 10 years out of power, he said they were "as hungry as a starving tigress on the prowl".
He told the conference: "Voters have to keep the Tories where they belong - out of office and out of power."
Mr Morgan warned his party that the opposition parties made "strange bedfellows," but they were willing to enter a triple alliance - or, as he joked, "a tripe alliance".
He said that that "nightmare alliance could be running Wales after 3 May" and urged his party's supporters: "If you are Labour, vote Labour".
He spoke the day after Prime Minister Tony Blair - making his final speech to the Welsh conference before stepping down this year - told delegates that a vote for any other party could lead to a "rag-bag Tory-led coalition".
Mr Morgan continue the attack by warning against letting the Tories get into power "through the back door".
The conference ended in time for delegates to watch Wales' Six Nations match against France.
Mr Morgan, a rugby fanatic, quoted Welsh coach Gareth Jenkins, who has called for "more grunt up front," and urged Labour activists to follow suit.
Nick Bourne, leader of the Conservatives in the assembly, said Mr Morgan's speech "lacked vision, big ideas and conviction".
"It exposed in the clearest possible terms how Rhodri Morgan and Labour have run out of energy and are running out of time," said Mr Bourne.
"We heard nothing new from Rhodri Morgan in this speech. While all he can do is talk about the past the Conservative Party is looking to the future."