By Steve Schifferes BBC News Online Washington correspondent

As fog and rain descended over Washington, the crucial summit between Tony Blair and George Bush was moved from the ice-bound Camp David retreat in Maryland to the White House.

Some of the greyness outside seemed to carry over in the sombre and even tense mood of the joint press conference, which was first delayed, and then abruptly ended by President Bush after only 15 minutes.

It is essential that in every respect, in every way that we can, we mobilise international support and the international community UK Prime Minister Tony Blair

It was clear that these had been difficult discussions, with critics of the rush to war - both at home and abroad - hoping that the prime minister was going to be moderating influence.

Both leaders agreed that Saddam must be disarmed "in weeks not months" and that he was not fully co-operating with the UN inspectors as specified by UN resolution 1441.

The message seemed to be that war was imminent; several times it was left to Mr Blair to spell out exactly why Iraq was in breach of its obligations and a threat to the world community.

To some extent, this is the role the two leaders have played in the past, with Mr Bush's blunt talking contrasting with Mr Blair's quiet and more legalistic reasoning.

But behind the scenes, Mr Blair has been arguing for more emphasis on diplomacy in the final few weeks, in order to secure the endorsement of the United Nations before hostilities commence.

This, the British believe, could be vital in securing more help from allies in the Middle East and more support from a sceptical European public, while the troop build-up continues.

Diplomatic question

While Mr Bush praised Tony Blair as "a friend of the American people" and said he trusted his judgement and appreciated his wisdom, his remarks revealed an impatience with the diplomatic process that did not seemed fully shared by the prime minister.

Tony Blair had earlier spoken of his desire for a second UN resolution to authorise war. He repeated: "It is essential that in every respect, in every way that we can, we mobilise international support and the international community."

However, the president put his answer on any future UN resolutions in the context of avoiding any further delays.

"Should the United Nations decide to pass a second resolution, it will be welcomed if it is another signal that we're intent upon disarming Saddam Hussein. 1441 gives us the authority to move without a second resolution," he said, stressing in his tone the conditional nature of his approval.

Special relationship

Privately, British officials believe that they have secured agreement that the US will work for that second resolution - although the official US position, as spelt out by top State Department officials on Thursday, remains that it is "desirable but not necessary".

Now the time for diplomacy is rapidly running out, with the prospect of further UN endorsement still unclear.

The UK clearly still hopes to mobilise the international community behind the overthrow of Saddam Hussein.

But it is clear that, whatever his concerns, the prime minister has firmly linked his fate to that of the president.