PARIS -- France's presidency of the European Union got off to a rocky start Tuesday with Poland baulking at a key treaty and President Nicolas Sarkozy in a public spat with European trade chief Peter Mandelson.

Unpopular at home, Sarkozy had hoped to shine on the international stage but the six-month French EU presidency was hobbled even before it began when Irish voters last month rejected the Lisbon Treaty in a referendum.

On Tuesday, the bloc took a fresh blow when Polish President Lech Kaczynski said that after the Irish "No" he refused to sign the treaty that was aimed at streamlining EU decision-making.

That decision put Kaczynski alongside his Czech counterpart in seeking to delay final ratification of the charter -- which must be ratified by all 27 EU states to take effect -- while Germany also faces a legal hurdle to final approval.

Sarkozy personally called on Kazcynski to ratify the EU treaty, reminding him that he had signed the charter at a summit in Lisbon in December.

"We have signed on behalf of our countries to ensure that Europe moves ahead and we must live with the consequences of the signature," said Sarkozy.

"I cannot imagine that the president who has signed his name at the bottom of the document in Brussels first, and Lisbon later, can cast doubt on his own signature."

On top of the Polish bombshell came an angry statement from Mandelson's spokesman saying that Sarkozy's latest "attack" on the British commissioner was "wrong and unjustified."

Mandelson himself, in Paris along with European Commission president Jose Manuel Barroso and other EU commissioners to mark the start of France's presidency, said that "at a time like this when the EU is entering a tough negotiation, we need unity, not division."

Sarkozy has long been fiercely critical of the EU trade commissioner, accusing him of offering too generous concessions on farming in fraught negotiations at the World Trade Organization.

He renewed his criticism during a television interview on Monday, suggesting Mandelson was trying to force an unfavorable trade deal on Europe.

But on Tuesday he played down the row, saying "it's not forbidden to have disagreements in Europe" even as Mandelson skipped a dinner with EU commissioners to mark the beginning of the French EU presidency.

The energetic leader who proclaimed "France is back in Europe" after coming to power a year ago, had hoped to be able to concentrate on five main areas when France took over the EU presidency from Slovenia.

These are immigration, defense, energy and the environment, agriculture, and the most high-profile project: the July 13 launch of a new Union for the Mediterranean.

But his top priority will now be to salvage the Lisbon Treaty and push EU states to continue ratifying it before the June 2009 European parliament elections.

Sarkozy had been due to travel to Ireland on July 11 to hear at first hand the concerns of voters there. But he said Tuesday he was delaying that trip until July 21 due to scheduling problems.

EU leaders are to re-assess the fate of the treaty at a summit in October at which Irish Prime Minister Brian Cowen will present his ideas on the way forward.

The EU's blue flag with gold stars was flying high in Paris for the first day of the French EU presidency and the Eiffel Tower was also lit up in EU colors.