Mr Morgan said longevity ran in his family

Speaking ahead of the fourth anniversary of taking on the leadership of the Welsh assembly, Mr Morgan, 64, said he was in full health and would carry on until he stopped "enjoying the job" - or until voters decided otherwise.

The greatest achievements under his reign, he said, had been massive improvements in employment and education but he admitted the health service, particularly waiting lists, had been more problematic.

But both the main opposition parties, Plaid Cymru and the Conservatives, said Mr Morgan had nothing to "crow" about.

He felt his main achievement was introducing a "new kind of politics" to Wales, where ministers were more approachable.

On possible retirement, he said: "I'm very conscious of Gareth Williams' [former House of Lords leader Lord Williams of Mostyn] death suddenly at 62 and it's made me very determined to enjoy the job.

"When I stop enjoying the job, I'll stop doing the job.

I tend to think you get burnt out not because of your age but the number of years you've been on the front bench Rhodri Morgan

"There again others might stop me doing the job because you have to submit yourself to the test in a election.

"But my mother's almost 98 so there's a lot of longevity in the Morgan family and basically I've only been a minister for four years.

Mr Morgan, who was an MP from 1987 to 2001, became Welsh Labour leader when First Secretary Alun Michael resigned in February 2000.

"I tend to think you get burnt out not because of your age but the number of years you've been on the front bench, the number of years you've been a minister," said Mr Morgan.

"In that sense I haven't been a minister very long and I think I've got a long way to go, but it's for others to say.

"Every so often political careers for first ministers and prime ministers, or any other kind of minister, come to an end because your political colleagues tell you your time's up, it's time to make way for somebody new.

"Or the people tell you by defeating your party in an election," he added.

'Cheap plonk'

His four years in office have been marked by an inability to take the tough decisions needed to improve life for the people of Wales Nick Bourne, Conservative leader

"Now I'm hoping 2007 won't bring such a message to me because I think I've still got a lot to do and lot more to offer."

He said his administration had been surprised at the rate of development in some areas.

"In education, I think progress has been very rapid, but in some ways that's connected with the fact that you have a falling number of children and therefore it's easy to carry out education initiatives.

It worked the other way with health, Mr Morgan explained, as there were rising numbers of pensioners putting "increasing pressure" on the service.

"Maybe we didn't take enough account of the changing shape of Wales but overall I think the strategies we've got in place are paying off.

"But some are taking longer to pay off than we thought," he added.

Plaid Cymru's assembly leader , Ieuan Wyn Jones, said: " It is the achievements or lack of them in government that should be examined, not someone's length of time as leader.

"I'm afraid that according to that yardstick Rhodri Morgan has nothing to crow about regarding the last four years."

Nick Bourne, who leads the Tories, said: "Rhodri Morgan's promise to 'open the bottle of Welsh champagne and let it fizz' went flat pretty quickly.

"All we got was a cheap bottle of plonk from the local corner shop.