If successful, it could lead to a seamless transition from his current job as "high representative" for the European Union's common foreign and security policy to the continent's top diplomat.

At least, that is the hope. But while Mr Solana, appointed in 1999, also has support from Berlin, London and other capitals, the assumption of a seamless transition could be wishful thinking.

This is because of the complicated provisions set out in the draft treaty for Europe's first constitution, which the European Union's 25 leaders hope to agree next month.

So, as Spain follows other countries to push for its preferred candidate for one of the EU's top jobs, it raises broader questions over when and how the new foreign minister could operate.

The role of foreign minister is important since he or she will be responsible for presenting to the outside world Europe's security, defence and foreign policies. It will also differ fundamentally from the present way foreign policy is conducted.

Mr Solana, working with an annual budget of about 47.5m ($57m, £32m) and a small staff, is beholden to the member states that jealously guard their foreign policy. The Commission, the EU's executive arm, has its own external relations chief, Chris Patten, who has an annual budget of 7bn, a big staff but little power.

To give the EU a more coherent foreign policy, the new constitution would combine both jobs, making the vice-president of the new European Commission, to be in place by November, the foreign minister.

In practice, the foreign minister would sit in the Commission with access to money and a large diplomatic service. On defence and security issues, the minister would answer to the Council of Ministers (the member states) since they will not cede such matters to the Commission.

This means the minister will be answerable to two masters, raising some questions over how effective this person can be. "Much will depend on the personality of that minister," said a Dutch diplomat.

Another issue is when the foreign minister's job will become a reality. Some countries want the job to begin this November, the same time as the new Commission. But the foreign minister's job is part of the constitution. It may have to wait until the constitution is ratified or even until 2009, the date for its implementation. "We cannot wait until then. Europe desperately needs a foreign minister more than ever before," said a French diplomat.

A possible compromise is that states agree to bring forward the foreign minister's job after ratification. Until then, Mr Solana, should he want the job, will continue as now and the Commission vice-president will be the external affairs commissioner.

Ireland, which holds the EU's rotating presidency, hopes to decide the top Commission and council jobs at next month's EU summit.

If Mr Solana wants to be foreign minister, he will need to seek assurances that the starting date happens as soon as the constitution is ratified. And he will need to know that the Commission's vice-president for external relations will resign. "After all, when it comes to foreign policy, one person has to lose out after ratification," said a British diplomat.