Negotiations with NATO that would bring Ireland into membership of Partnership For Peace are expected to open within months.

Ireland's involvement in Partnership For Peace will cover "peacekeeping only" and not peace enforcement, a Government spokesman has said.

Following the announcement by the Taoiseach, Mr Ahern, yesterday that he envisaged Ireland joining Partnership For Peace "in the second half of this year", a spokesman said "the wording of our membership makes the level of our participation quite clear".

"It is for peacekeeping only", he added.

The Government is also insisting the move does not require a constitutional referendum. Sources said the Minister for Foreign Affairs, Mr Andrews, will proceed to get Government approval to begin negotiations on membership within months. The negotiations will be conducted between the Department and NATO and the final agreement will be brought back to the Dail for approval. "The agreement will be tailor-made so that we can choose a la carte. It will only involve peacekeeping", a senior source said.

In spite of a widespread expectation that the Government was moving towards involvement in PFP, the Taoiseach's Dail announcement of a firm timetable that would lead to actual membership by the end of the year came as a surprise to many TDs, not least in his own party. However, it emerged last night that Mr Andrews had briefed Cabinet on the matter in recent weeks.

Apart from the Green Party and Sinn Fein, there was little immediate political opposition to the prospect of membership. However, Labour sources said they expected the party to join the opposition to PFP as soon as it formally discusses the matter at its conference in May. A position paper on the matter is being prepared by the new foreign affairs spokesman, Mr Proinsias De Rossa.

Angrily accusing Mr Ahern of reneging on Fianna Fail's pre-election promise by "attempting to sneak Ireland's membership in the back door", the Green Party TD, Mr John Gormley, said it would involve an agreement negotiated directly with NATO "and Irish officers will serve in NATO military headquarters".