European Union leaders are expected to approve a treaty on E.U. reforms during a meeting in Lisbon Thursday and Friday. Lisa Bryant reports from Paris that if signed and ratified, it will end a two-year political crisis.

The treaty is the fruit of a long and bitter debate. It aims to reform and streamline European Union institutions and give more cohesion and power to the 27-member bloc.

There are still unresolved issues. Poland wants changes to E.U. voting rules. Italy is not happy with the allocation of European parliament seats. But many of the larger stumbling blocks were resolved at a June summit in Germany.

An analyst at the Center for European Reform in London, Hugo Brady, says agreement at Lisbon on the new treaty is by no means certain.

"There are a number of issues hovering around the summit, but none of which on its own I would expect to crash the summit or collapse the negotiations," said Brady. "Because the reality is, the reason why these issues all seem so small and petty, is because the real flesh and blood of this negotiation has already been gotten over last June."

The new agreement would extend the E.U. rotating presidency to a two-year term. It would also give the E.U. greater say in foreign and internal security policy.

But it is far less ambitious than a draft European constitution that members previously agreed on. The constitution was put on hold in 2005, after French and Dutch voters rejected it in referendums.

Even if agreed on by member nations, this latest treaty must still be ratified by all 27 E.U. states. Analyst Hugo Brady says that is not a sure bet.

"I think for any set of reforms in the future the question should not be: is there any chance of them not getting through? The question should be: after the votes in 2005, is there any chance of them getting ratified at all?" said Brady. 

Supporters argue that a new treaty is essential to enact critical reforms in the European Union and allow it to grow in the future. But skeptics argue the bloc has carried on to date without a new treaty.