The post becomes vacant later this year when Javier Solana steps down to take over a new post as foreign policy co-ordinator for the European Union.

Nato officials said a consensus has been building behind the Scottish minister, whose surprise nomination was announced by Tony Blair on Friday.

The UK prime minister said: "George has exactly the right mix of defence expertise and political and diplomatic skills."

Mr Robertson stressed he was just a candidate, but added: "I started out in politics wanting to create a safer world for future generations.

"If I am appointed, I will be given a unique opportunity to make something of the great opportunity around today and the challenges facing Nato."

US backing

The White House says it is pleased with Mr Robertson's candidacy and US Defence Secretary William Cohen told reporters: "(Robertson) will have wide support."

Mr Blair is also said to have positive responses from several other Nato leaders including French President Jacques Chirac, Italian Prime Minister Massimo D'Alema and Spanish Prime Minister Jose Maria Aznar.

Cohen: 'Robertson has our support'

Mr Robertson, 53, has impressed the allies with his robust stance and adept media presence during the Kosovo conflict, and for his work on preparing reforms for Britain's armed forces.

The previous favourite for the job, German Defence Minister Rudolf Scharping, has also made it clear he wants to stay in the German Government.

Several other names have been mentioned in press speculation among them the former Belgian Prime Minister Jean-Luc Dehaene and Hans Haekkerup, Denmark's defence minister.

Strong contender

Nato spokesman Jamie Shea said Mr Robertson was highly thought of in alliance circles, but the appointment was not a foregone conclusion.

He said: "He is an excellent candidate. The UK by putting him forward has signalled its interest in seeing obviously a very capable, very strong secretary general of Nato to take up the work of Javier Solana. But of course, he is only a candidate."

Blair says his defence secretary has 'right mix of skills'

Mr Robertson said the main challenges facing Nato were enlargement, dealing with the Russians and strengthening the European defence identity.

"We also have to build relations with Russia and see how Nato can be enlarged in future years so we can give common security to another generation, like my generation has benefited from in the last 50 years," he said.

Political impact

If Mr Robertson is picked to replace Javier Solana he would have to leave the cabinet, prompting further movements within the government.

There has been speculation he will be replaced by the present Scottish Secretary, Dr John Reid, who in turn would be replaced by junior Scotland Office minister Brian Wilson.

It would also trigger a by-election in the Scottish MP's Hamilton South constituency which he has represented for 21 years.

Mr Robertson was appointed to his current job following Labour's general election victory in 1997. During his time in opposition he served as Labour's spokesman on Scottish affairs, and then on foreign and defence issues.

The post of secretary-general, Nato's top civilian position, is traditionally held by a European politician, while a US general serves as alliance military commander.