The Taoiseach appears certain to nominate Mr Brian Cowen to replace Mr David Andrews as Minister for Foreign Affairs in a potentially wide-ranging reshuffle of his Cabinet and junior ministers.
The Minister for Education, Mr Martin, is seen as most likely to replace Mr Cowen in Health, and one or more other Ministers may change portfolio.
Just one new Cabinet member is expected to be appointed from among the Ministers of State. However, Government sources say two Ministers of State may be demoted, giving Mr Ahern the opportunity to appoint three backbenchers as junior ministers.
Meanwhile, The Government is likely to nominate Mr Justice Ronan Keane of the Supreme Court to replace the retiring Mr Justice Liam Hamilton as Chief Justice when it meets in Cork tomorrow.
A leading barrister, Mr Adrian Hardiman SC, is tipped for nomination to one of two Supreme Court vacancies.
While Mr Andrews will formally hand the Taoiseach his resignation as Minister for Foreign Affairs on Wednesday, the Cabinet reshuffle may not be announced on that day. The President, Mrs McAleese, who must formally make Cabinet appointments, will be out of the State and will not return until Thursday night or Friday.
Government sources say Mr Ahern may want Mrs McAleese, rather than the Council of State, to preside over the formalities.
The Government Chief Whip Mr Seamus Brennan is lobbying hard for promotion to Cabinet. However Mr Ahern is reluctant to move him, having told colleagues he is doing his present delicate job very well.
Mr Brennan is responsible for relations with the four backbenchers who support the Government in tight votes. Replacing him could jeopardise that finely-balanced relationship, leading to instability for the minority coalition, Mr Ahern believes.
The Minister of State, Mr Martin Cullen, is among those tipped for promotion to Cabinet should Mr Brennan be passed over.
With the prospect of the appointment of three new Ministers of State emerging, Fianna Fail backbenchers such as Ms Mary Hanafin, Mr Eoin Ryan, Ms Marion McGennis, Mr Sean Ardagh, Mr Pat Carey and Mr Billy Kelleher are among those seen as contenders.
Mr Cowen is seen as a virtual certainty for foreign affairs. He is highly regarded by the Taoiseach, who also believes he should be rewarded for doing a difficult job for over two years. While Mr Martin has a positive public profile in the education post, he is said to be keen to prove his political abilities in a more difficult department.
He has told the Taoiseach he would be happy to move, and is widely tipped to replace Mr Cowen at Health, although in the event of a wider reshuffle a move to a different department cannot be ruled out.
If Mr Martin moves to health, Mr Ahern could confine his Cabinet changes to these two moves, promoting a new Cabinet Minister to fill the education post. However, even if he moves Mr Martin to Health, there is speculation that he may move another Minister - currently in a less prominent job - to Education and promote a backbencher to the less prominent position.