Two of the most effective, high-profile diplomats in the Foreign Service have swapped jobs this week in preparation for the next phase of the Northern Ireland peace process and negotiation of a three-stranded settlement embracing both islands.

Sean O hUiginn, second secretary at the Department of Foreign Affairs with responsibility for the AngloIrish division, has been appointed Ambassador to Washington. And Dermot Gallagher relinquishes the Washington posting in favour of his old job, with a new ranking, in Anglo-Irish affairs.

Both positions are critical to Irish foreign policy at this time. And both men bring exceptional, if diverse, talents to bear on their responsibilities.

When news of Mr O hUiginn's departure to the United States was published in The Irish Times earlier this year, it was greeted with public relief and satisfaction by unionist politicians who had come to distrust and fear his intellectual capacity.

They called him "the Prince of Darkness". And they recognised his interfering hand and innovative thinking behind many aspects of the Downing Street Declaration and the Framework Document. They resent ed his ability to circumvent their arms decommissioning bulwark through the involvement of George Mitchell and by way of tough, intergovernmental negotiations. They regarded him as a "green bogeyman".

It is not how Mr O hUiginn is viewed at Iveagh House or within Government circles. Tough, yes. And deeply committed to securing a settlement that would embrace both communities. But his nationalism is defined on a cultural and social level. And he sees his role as one of problem-solving, rather than of uniting Ireland.

During his five years in control of the Anglo-Irish section, under Dick Spring, the Department of Foreign Affairs successfully resisted British and unionist pressure to compromise on issues Mr O hUiginn regarded as crucial. And he was highly regarded by senior Fianna Fail figures.

He developed a considerable rapport with Sinn Fein figures during the first IRA ceasefire and they regarded him as "an absolutely straight dealer".

But his forceful expression of Government policy and concerns led to friction with British government officials and with unionists. He was "immensely able and as hard as flint", according to a colleague. As a result, he was both disliked and highly respected by the British.

A senior Labour Party source regarded Mr O hUiginn as one of the two most impressive people he had ever met in the Irish public service. . .a man of immense intellectual capacity. . .a conceptualiser and innovator.

His appointment as Ambassador to Washington was delayed because of the inter-governmental negotiations on arms decommissioning leading up to the September talks process. The successful reinstatement of the IRA ceasefire was one of his last projects.

The move may complement the changing needs of Irish diplomacy. Mr O hUiginn's "in your face" nationalism and his strengths as an original thinker have played their part in creating the present opportunities. Dermot Gallagher's abilities as a consolidator and pragmatist may now come into their own in the September talks process.

Mr Gallagher is less aloof and more convivial than Mr O hUiginn. And his term as Ambassador to Washington coincided with a flowering of Irish influence on Capitol Hill and in the White House.

His cultivation of contacts extended even to unionist politicians, when they visited Mr Gallagher's residence during an Irish-American investment conference. And he developed formal and social contacts with a wide range of influential figures in the US.

As Mr Gallagher leaves Washington, where key officials in President Clinton's National Security Council - Mr Anthony Lake and Ms Nancy Soderberg - have been replaced, his successor has a whole range of new officials to cultivate. And there is the ever-present need to counteract British lobbying within the State Department.

Mr O hUiginn will see his task in the US as maintaining and reinforcing President Clinton's personal engagement with the peace process, as the Northern Ireland talks get under way. And, as an urbane intellectual with an attractive personality, he can be expected to burnish the achievements of his predecessor.

The new Anglo-Irish head resumes work this week in building relationships with representatives of the British Labour Party government in Downing Street and at the Northern Ireland Office. As a former boss of the division - and closely connected to Northern Ireland events through his Washington posting - Mr Gallagher will be aware of the pitfalls and opportunities.

The change was regarded as timely by one observer, who felt the basic ideas for a settlement are now in place and it was time for a consolidator, rather than an innovator, to play a role. Mr Gallagher was, according to a reliable source, "not as green as Sean" and was likely to be seen by unionists as "a bit more pragmatic and accommodating".

But the unionists also remember the flinty-edged Mr Gallagher from the days when he oversaw AngloIrish affairs and the unsuccessful three-stranded talks process under a Fianna Fail/Progressive Democrats government in 1991-92.

The face in charge of the AngloIrish division at the Department of Foreign Affairs may have changed. The policy endures.