Mr Morgan has previously said he intended to stay on as leader

Mr Morgan, 67, had previously said he would step down as first minister in around two years if he remained in the top job until that time.

But now he has indicated he would go sooner, if his party loses key seats in the assembly election on 3 May.

In earlier interviews he said he would stay until voters decided otherwise.

The former Cardiff West MP and assembly first minister for the past seven years told BBC Radio Wales: "I will know if we have lost badly, and I will retire and leave the stage because that's what all politicians - who have to accept the verdict of the electorate - do."

If people want me out they can get me out by voting against Labour Rhodri Morgan

Urging Labour supporters to vote in the third Welsh assembly election on 3 May, Mr Morgan put his leadership of the Welsh Labour and assembly government on the line.

"If people want me out they can get me out by voting against Labour," he told the Good Morning Wales programme.

"If they want Labour to continue, then Labour voters have got to come out and vote Labour - that's the key message."

Although past the official retirement age, Mr Morgan has long declared that he has no intention of relinquishing his first minister role until well into the next assembly term.

Three years ago, speaking ahead of the fourth anniversary of taking on the leadership of the assembly, Mr Morgan said he was in full health and would carry on until he stopped "enjoying the job".

Astonishing admission

In July 2005 Mr Morgan reaffirmed he would lead Labour into the election in 2007, but it was the "absolutely logical answer" to step down in 2009 if the party was successful.

"I am lucky to continue in good health and with an undiminished appetite for the business of government," he said then.

The leader of Conservatives in the assembly, Nick Bourne, said Mr Morgan's announcement was an "astonishing admission from a party leader so close to an election".

"He knows the writing is on the wall and that he will be out of a job in 28 days' time, " said Mr Bourne.

Plaid's deputy assembly leader Rhodri Glyn Thomas said it was generally accepted that Labour would do badly at this election.

"It seems that Rhodri Morgan is already acknowledging the inevitable."

Welsh Liberal Democrat assembly leader Mike German said: "Rhodri is acknowledging what we all know.

"He is a lame one-legged-duck first minister leading a shoddy administration that have run out of ideas."