By Nick Assinder BBC News Online political correspondent

We should make no mistake - the campaign to take military action against Saddam Hussein is now under way.

Tony Blair and George Bush have massively stepped up their efforts to win over a doubting world - just as they did before the action against al-Qaeda in Afghanistan.

The prime minister is flying out for a brief but absolutely crucial meeting with the President at Camp David this weekend.

Blair must persuade a doubting public

They will discuss the best tactics to adopt to build an international coalition similar to the one forged before the action in Afghanistan.

And it is inconceivable they will not discuss the exact nature of any military action against Saddam.

Tony Blair will then fly to Moscow next month to use his powers of persuasion on President Putin who is set against action.

New deadline

At the same time he is planning to produce his documentary evidence against Saddam and use speeches to the trade union and Labour conferences to try to turn the tide of opinion at home.

A recall of parliament to discuss action against Baghdad is now highly likely, with the only argument, albeit a crucial one, being over the timing.

Meanwhile, the president is suggesting he will want to get the UN on-side before he launches himself at Saddam.

And he is out to woo the members of the security council around to the idea of a new deadline over weapons inspectors.

Recall likely?

Much of this is the sort of stuff that many opponents to any war with Iraq have been demanding.

The US stance, in particular, is clearly aimed at suggesting - as Tony Blair continually claims - that the president is no gung-ho war-monger out to wreak revenge for 11 September.

Genuine threat

And if this campaign works then things might look fundamentally different in a few weeks time.

If the two leaders get their way, the UN will be on-board, public opinion will have swung behind them and Saddam will be under irresistible pressure to cave in.

However, the men have set themselves a huge task and there is plenty of evidence to suggest it will not succeed.

Doubters want the UN to be fully supportive of action, they want concrete evidence that Saddam is a genuine threat and they want an international coalition in support of action.

Saddam must cave in

Even then there are plenty who would still oppose military action and demand more diplomatic efforts, particularly aimed at the wider conflict in the Middle East.

Few believe Saddam will fall in line with deadlines on weapons inspections or, if he did, that he would not later continue to "stiff" the world. And that is clearly what the president and the prime minister believe.

Highest risk

So whatever the effect of the current diplomacy, most still believe one thing is a near certainty - there will be a military campaign against Saddam Hussein within months.

And this time, unlike the last Gulf war a decade ago, he will not be allowed to survive it as leader of Iraq.

War may not be an absolute inevitability, but it is increasingly difficult to see where Bush and Blair have left themselves an escape route.

Unlike the Afghanistan operation, however, this is the highest possible risk affair.

Both leaders have put themselves on the line over this one, but that is probably the least of worries.

If they get this wrong the consequences for the world are incalculable.