By Andrew Marr BBC News political editor

The Americans are said to be prepared to put more troops into Afghanistan, while the British forces already at Bagram airport outside Kabul may be pulled out again.

So what is going on?

The first thing to is to distinguish between troops being sent to fight and troops being sent to help aid workers, clear mines and enforce some kind of peace.

There may be more special forces if and when Bin Laden's hideouts are identified

As for the fighting - there are already British special forces and American special forces, plus CIA people, down in the south of Afghanistan, acting as spotters for the bombing and working in teams to try to track down Osama Bin Laden and al-Qaeda.

Is there going to be a larger force?

There may be more special forces if and when Bin Laden's hideouts are identified - indeed there are plenty of US marines waiting off the coast of Pakistan as well as those on the ground.

Conventional troops

But is there going to be a large conventional infantry force going into southern Afghanistan to continue the war?

No, almost certainly not.

That would anger the Northern Alliance and the majority Pushtun tribes, as well as being difficult to organise in terms of supplies and very risky

Up in the north - at places such as Kabul and Mazar-e-Sharif - it is a totally different situation.

The United Nations' blue helmets are still a likely option

Here, the buzz word is 'stabilisation' and in the end, senior government figures say, the United Nations' blue helmets are still a likely option. But that might be months away.

Between then and now two things are possible.

The first is that friendly Islamic states, working to the Organisation of the Islamic Conference, might put in people - the so-called 'coalition of the willing'.

Among those likely to be involved are the Turks, who have relatively strong connections to the states north of Afghanistan and to the Northern Alliance itself.

The Pakistanis, however, will want a broader force than that and this will also take some time to get going.

Fast moving

So we are left with the question of what happens soon.

It's a very fast-moving situation - as the uncertain position of the British SBS troops, with some Americans, at Bagram airport shows.

There is almost visible embarrassment around Whitehall at the delay there; one senior source said this week the 'second phase' of the Afghan crisis, after the military one, will be even more testing than the first.

It's a split perhaps between the quite keen, us, and the pretty cautious, the Americans, it's a question of degree

But most expect some British troops, plus perhaps some Americans, French, Germans and Italians to carry out a number of tasks, ranging from protecting food aid to clearing mines and rebuilding bridges.

It doesn't look likely, however, that they will form some kind of militarised police force.

One of the things that nobody expected was the Taleban to collapse so quickly.

But equally unexpected has been the Northern Alliance's relative self-discipline and their ability to maintain order in Kabul.

Now, if there is a split between the UK and US I think it's a split about enthusiasm.

It's a split perhaps between the quite keen - us - and the pretty cautious - the Americans. It's a question of degree.

Gladstonian

There is no doubt that right from the beginning of this conflict London, Tony Blair, had been much keener on the 'Gladstonian' business - 'we will never turn our backs again'.

Whereas the Americans have been much more focused on getting al-Qaeda, getting Osama Bin Laden: 'Kill these guys and then we think about what we do next'.

It's a question of emphasis.

Now over the next few months the second phase of all of this will become increasingly acute, and perhaps politically difficult, but at the moment the question is: are they going to put stabilisation forces in?

And the answer is: probably, but it's going to take a while and they will not look like a Western army of occupation - almost everyone agrees that would be disastrous.