Fine Gael called on the Government and the international community to admit that the decision to attack Serbia was a political decision without legal authority.
The party's leader, Mr John Bruton, said it was better to be honest than to pretend there was a "spurious legal authority when none exists". He was concerned that the initiative to attack had not been thought through.
Labour's foreign affairs spokesman, Mr Proinsias De Rossa, called for the Government to "get off the fence" and "politely but firmly" oppose military action.
His party colleague, Mr Michael D. Higgins (Lab, Galway West), said comments by the Minister for Foreign Affairs, Mr Andrews, in Berlin that Ireland was caught between "a rock and a hard place" were a "pathetic response".
However, the former Progressive Democrat leader, Mr Dessie O'Malley, said it was easy to take the view that any form of violence and force was of itself wrong. "We should begin from the premise that the appeasement of tyranny is one of the greatest mistakes the world has made in the past."
The Minister for Defence, Mr Smith, opening the debate, said that the international community "has done its utmost to find a peaceful solution to the Kosovo conflict".
Mr Smith pointed out that more than one quarter of a million people were now homeless because of the repression carried out by Serbia's security forces. Some 65,000 had been driven from their homes in the last month and 25,000 since the peace talks broke down.
"While the Kosovo Albanians signed the Rambouillet accords, Belgrade's forces poured into Kosovo to start a new offensive," he said. "The civilian population is the target of the hostilities."
Mr Bruton said everyone should be honest enough to admit that the quoted UN Security Council Resolution 1199 did not authorise the operation. "Whatever may be claimed by NATO, there is no mention of the use of force in that resolution. We should not stretch credibility too far in making such a claim."
He said there was a likelihood that the bombing would aggravate the civil war and there could be one million refugees within the next two weeks.
He pointed out, however, that President Milosevic had caused the original problem by extinguishing Kosovan autonomy and that had led to the "current dreadful situation".
The gravity of the situation should not be underestimated he said, pointing out that the Federal Yugoslav army was bigger than either the British or French army.
Mr De Rossa said it was a sad day for Irish foreign policy. "We have what amounts to a full-scale war in Europe for the first time for 45 years, yet the Irish Government apparently has nothing to say on the matter.
"Countries like Austria, which have come out strongly against the NATO attack, have shown that it is possible to be a member of the European Union without losing your voice."
He said the military action was a serious misjudgment and "has already shown signs of reopening cold war divisions between Russia and the West and will certainly lead to increased tensions in the Balkans".
"We should get off the fence and say politely but firmly to our friends in Britain and the US that we do not consider military action to be appropriate at this time or in these circumstances."
Mr Caoimhghin O Caolain (SF, Cavan-Monaghan) registered Sinn Fein's opposition "in the strongest possible terms" to the attack on Serbia. "This is undoubtedly the most serious act of international military aggression within Europe since the end of the second World War," he said.
"All previous experience shows that military intervention by foreign powers will serve only to deepen the national social divisions in the region and postpone the prospect of a peaceful longterm solution."