European leaders are preparing to meet in Brussels Thursday for the start of a summit the could determine the fate of the euro.

Some officials have described the European summit as a moment of reckoning for the common currency, under siege by the continent's ballooning debt crisis. But as the opening of the meeting draws closer, optimism is waning.

A plan detailed Wednesday by German Chancellor Angela Merkel and French President Nicolas Sarkozy calls for all 17 nations using the euro to adhere to balanced budgets and enforce strict penalties on violators. It would also create a unified corporate tax rate and a new financial transaction tax.

Finally, the plan seeks to streamline the EU bailout fund in order to respond more quickly to future crises.

But senior officials said late Wednesday that final agreement on a deal could be weeks away. One German official told the Associated Press that it might be Christmas before a deal is reached. Another senior official was quoted as saying that some countries “have not understood the seriousness of the situation.

Fears that Europe's debt crisis could spark additional problems have sent jitters through the global financial markets and have prompted warnings from several top credit rating agencies.

U.S. President Barack Obama spoke with German Chancellor Angela Merkel by telephone late Wednesday.

The White House said President Obama and the German chancellor agreed on the need to find a lasting and credible solution for the eurozone crisis. The U.S. president has repeatedly urged European leaders to do what is necessary to fix the crisis as soon as possible.

German Chancellor Merkel and French President Sarkozy said the new EU treaty provisions should be ready for adoption by March.

But Britain, which does not use the common euro currency, has indicated that it may not be willing to sign on to the new EU treaty provisions. Prime Minister David Cameron said earlier this week that he will defend Britain's interest at the summit in Brussels.

All 27 EU nations have to agree on any changes to their treaty. If other non-eurozone countries follow Britain's example, only the 17-nation bloc that uses the euro might agree to more centralized authority over budgets.

U.S. Treasury Secretary Timothy Geithner, fearful of the effects of a euro collapse on the fragile American economy, has been on a three-day trip to European capitals to push European officials to adopt strong measures.

After meeting with French Finance Minister Francois Baroin in Paris, Geithner expressed confidence that the European officials will move to control government spending, create new economic growth and calm jittery financial markets worried about governments defaulting on their debts.