The bombing in Kabul yesterday underlined the grip of the Afghan insurgency and came at a politically treacherous time for Barack Obama as he decides how to turn the tide of the war. A flurry of consultations and discussions on Afghanistan is under way in Washington as a prelude to a strategy decision. The President yesterday talked by phone with Gordon Brown about the situation, and today there will be further debate with his national security team.

Amid deeply conflicting views over troop levels, the only thing on which there is consensus is that whichever path the President takes, there are potential pitfalls. Choosing the wrong option may fatally undermine his authority and the rest of his presidency.

The decision made in Washington also carries profound repercussions for other Nato countries involved particularly Britain, as well as far-reaching consequences in a violent and volatile region.

US officials have made it clear that in return for President Obama putting even more American troops in the line of fire, other Nato countries would be expected to step up their contributions and loosen some of the caveats which prevent them from fully taking part in operations.

Even before Mr Obama makes his decision in Washington, Britain is likely to send another 1,000 soldiers to join the 9,100-strong force that is already on the ground in Afghanistan. The French and the Germans are believed to be prepared to send more troops while the Canadians may switch some of their forces from combat to training duties.

In the end, everything depends on how Mr Obama decides to conduct his first war as the leader of the West. The stakes could not be higher.

Troop surge

General Stanley McChrystal, pictured below, was hand-picked to combat the rejuvenated Taliban and has presented a damning assessment that warns the mission is likely to result in failure within a year without urgent reinforcements of between 20,000 and 40,000 troops. His blueprint would have Nato troops living among the people and safeguarding populated areas instead of flying off to fight the insurgents in the mountains.

The General also wants the numbers of Afghan security forces increased. The size of Afghan army would also be raised from 92,000 to 240,000, and the police from 82,000 to 160,000 by 2012. In addition he wants a concerted drive to win over Taliban fighters and has appointed the British commander, Lieutenant-General Sir Graeme Lamb, to carry through the "reconciliation" process.

Taking the McChrystal path would necessarily equate to a long-term commitment, a prospect that is already provoking significant levels of opposition in Washington. More troops, and the way the General wants them to carry out their missions, would inevitably mean more deaths. The spectre hanging over President Obama is that of Vietnam; thousands of troops mired in a long and bloody war with body bags coming home every week.

Counter terror

An alternative plan, outlined by Joe Biden, the US Vice President, pictured far right, opposes large-scale reinforcements and wants the focus to switch to counter-terrorism from counter-insurgency.

This would involve concentrating on hunting al-Qa'ida and its affiliates on the Pakistani border, carrying out Predator strikes inside Pakistan, and training Pakistani forces while moving away from the ambition of nation-building. Biden and his supporters hold that the Afghan Taliban are not a direct threat to the US.

This proposal has gained widespread support among powerful Democrats including House Speaker Nancy Pelosi, and Senator Carl Levin, chairman of the armed services committee, who have warned against further commitment without a clear endgame in sight.

Questions are also being raised about why Western lives are being sacrificed to prop up the government of Hamid Karzai, which is increasingly being seen as corrupt. But US and British commanders see worrying echoes between what Biden is advocating, and the "light touch" promoted by Donald Rumsfeld and Dick Cheney in Iraq. Their opposition to large-scale deployment was seen as a major contributing factor to Iraq descending into anarchy. The Biden plan, many senior officers believe, would spread insecurity in Afghanistan, with the Taliban forming de facto local administrations, while public opinion inside Pakistan would be further inflamed by what will be seen as yet more foreign interference.

Third way

The US administration has the option of broadly sticking with the status quo, and continuing to attempt to wring a small number of extra forces out of reluctant European allies while building up Afghan forces in the current haphazard way. Contrary to some reports, even Biden is not proposing an actual reduction in the number of American troops, nor is he opposing the already agreed deployment that will bring the numbers of US troops up to 69,000 by the end of the year.

What he favours is a shift in the type of operation that is being carried out by existing forces. Biden's advisers talk of sending in more special forces instead of regular troops and making much more use of unmanned Drone aircraft. However, the status quo will not satisfy either side in the debate and is unlikely to be seen as the leadership Barack Obama is now being asked to provide in the war.

Likely outcome

It is highly improbable that, despite the President's current hesitation, he will ignore wholesale the McChrystal recommendations. The military hierarchy is backing McChrystal and he is also getting some support, albeit more cautiously, from the highly influential Defence Secretary, Robert Gates. However McChrystal will not get all he wants. The President will probably authorise a further deployment at the lower end of the McChrystal request and the campaign against al-Qa'ida will be given much greater prominence. Gates is said to be in favour of such a compromise. The risk in this approach, say critics, is it will recreate a past, and unsatisfactory, scenario in which some American troops were hunting al-Qa'ida under Operation Enduring Freedom while others operated under Nato rules in the ranks of Isaf (International Security Assistance Force). The Americans, meanwhile, are expected to demand systemic reforms in the Afghan army and police. The training regime would become more thorough with Afghan forces given heavier weaponry. A pattern under which soldiers can use bribery to avoid serving in the violent south and east of the country would also be overhauled.

Separately, militias are likely to be formed to take on the Taliban and their allies, with some similarities to the "Sunni Awakening" groups that were paid to switch sides in Iraq.