The EU faced a new obstacle in its bid to salvage a reform treaty as leaders said on Friday Prague had a problem quickly ratifying it after Ireland's "No" vote.

The 27-member European Union now faces months of further uncertainty over the Lisbon Treaty originally meant to put an end to more than a decade of institutional wrangling and bolster the bloc's economic and political voice on the world stage.

Most leaders sought to put a positive spin on the outcome of a two-day summit, noting that ratification of the treaty by other countries would continue and they would review the way forward together with Ireland at their next meeting in October.

"Our agreement gives a very positive impulse towards the final solution," Slovenian Prime Minister Janez Jansa, who chaired the summit, told a closing news conference.

However a footnote added to the final declaration noted a new potential stumbling block in the Czech ratification process:

EU leaders acknowledged the Czech Republic could not complete ratification until its constitutional court rules, probably not before October, on whether the treaty is in line with its constitution.

The treaty is designed to give the bloc stronger leadership and institutions to cope with recent and future enlargement.

Prime Minister Gordon Brown said he expected all the other 26 member states to ratify the text and Ireland to come back to its partners with ideas for the way forward in October.

Traditionally Eurosceptical Britain raised EU spirits this week by concluding parliamentary ratification but a high court judge advised Brown on Friday not to complete the process until he had ruled on a civil suit demanding a referendum.

French President Nicolas Sarkozy, who inherits the issue when France takes on the rotating EU presidency on July 1, pointed to the risk of contagion.

"Ireland is a problem. But if we had a second or a third problem, it would become very difficult to solve," he said.

"A renegotiation of the treaty is out of the question. We are not going to redo a second simplified treaty," he said, noting the Lisbon Treaty was itself a boiled-down version of the EU constitution rejected by French and Dutch voters in 2005.

DEAD?

All 27 member states must ratify for it to take effect. The Czechs, whose Eurosceptical centre-right Civic Democrats are concerned about national sovereignty, had sought to prevent any call for continued ratification after the June 12 Irish referendum defeat.

Czech President Vaclav Klaus declared the treaty "dead" after the Irish vote and the Senate has referred the text to the constitutional court.

"We are a democracy - even the head of state is allowed his own opinion," Foreign Minister Karel Schwarzenberg joked. The independent pro-EU minister said he still thought his country would endorse the text by year-end.

Prime Minister Mirek Topolanek, seen as less keen on the treaty, said earlier: "I am not going to force members of parliament to back Lisbon and I would not bet 100 crowns (4 euros) on a Czech "Yes"."

The treaty would give EU leaders a long-term president, a stronger foreign policy chief with a real diplomatic service, a more democratic decision-making system and more say for the European and national parliaments.

Sarkozy and German Chancellor Angela Merkel insisted that without the Lisbon treaty there could be no further enlargement of the Union - a view contradicted by Jansa, Polish Prime Minister Donald Tusk and others.

Austrian Foreign Minister Ursula Plassnik said the EU must keep its word to aspirants for membership in the Western Balkans and Croatia, top of the queue to join, should not become the first victim of the Irish referendum.

Solutions mooted include offering assurances to the Irish that the Lisbon Treaty will not undermine their cherished neutrality, deprive them of a commissioner in Brussels, make abortions easier or raise taxes - and then asking them to vote again, as happened once before over an earlier EU treaty.