On the whole, I know what Russia should do, and how it should act," President Vladimir Putin said on Monday when he addressed parliamentary leaders in Moscow.

He was referring to one of the toughest decisions of his career: the degree to which he co-operates with the US in its campaign against international terrorism. He acknowledged the decision "has a very serious meaning for Russia's position in the world and in the future".

Late on Monday night Russia's contribution to the expected US attack on Afghanistan was pointing to a determination to stick to a non-committal, power-broking role.

Mr Putin went on television to say Russia would support the US military operation by funnelling arms to the Afghan opposition and opening its airspace for aid shipments.

In a five-point plan he said Russia was ready to offer its airspace for aircraft carrying humanitarian supplies to regions where "anti-terrorist" operations were being carried out.

Mr Putin also said Russian intelligence services would pass on information on "the infrastructure, the places where international terrorists stay and [their] fighters' training bases".

By holding back from direct involvement Mr Putin hopes to balance the rewards of a new relationship with the West against potential drawbacks of domestic dissent, diminished external influence and increased regional instability.

For Boris Nemtsov, leader of the Union of Right Forces parliamentary coalition, the opportunity to participate in an international coalition against terrorism represents "a rare chance to become part of the civilised world".

Yet others, including but not limited to Vladimir Zhirinovsky, the extreme nationalist deputy with links to the Iraqi leader, Saddam Hussein, argue for keeping a firm distance from the US.

Failure to do so, they claim, risks jeopardising Russia's links to the Muslim world and ignores the history of US involvement in helping create the Taliban regime. It could make Russia vulnerable to terrorist retaliation and draw it into fighting to protect its southern borders.

While most Russians expressed outrage at the attacks in the US, many - particularly those brought up in the shadow of the Soviet Union's occupation of Afghanistan in 1979-1989 - are wary of any repetition of the past.

That includes many military figures - including Anatoly Kvashnin, chief of staff - who have appeared to rule out the involvement of Russian forces in a campaign in Central Asia.

But it seems clear Mr Putin is making the decisions, and has been balancing the advantages and drawbacks of at least three options.

The first is increased cross-border sharing of intelligence and strategic expertise in the struggle against international terrorism. The second is granting access to the region for the coalition via Russia and Central Asian states under its influence.

A more extreme option would be direct Russian military participation in an assault on Afghanistan, with Western forces, or unilaterally.

Mr Putin has indicated the exchange of intelligence already exists and he is willing to see such links intensify.

To do so allows him to sustain his argument that Russia has been fighting the same struggle against terrorism through the conflict in Chechnya where, he says, rebels have been supported by radical Islamic groups from abroad.

But the war against Afghanistan, at least as painful for Russia as Vietnam was for the US, has left many veterans believing that a new conflict would be equally bloody and ultimately inconclusive.

Just as important, Russia already has heavy troop commitments in Chechnya. Although Mr Putin is only allowing an air corridor over Russia for humanitarian assistance, he has stressed the Central Asian countries are independent, giving himself the scope to distance himself from any choice to grant such rights to the US by Tajikistan, Uzbekistan or Turkmenistan.

Judging by the praise of Mr Putin by US President George W. Bush on Monday, Russia's limited support appears to satisfy US needs.

The reality is that, given the present mood and Mr Putin's apparent desire to orient himself and his country increasingly towards the West, he may have had little choice but to concede ground. The US is determined to act, and Russia's best interests may be served by capitalising on it instead.

Yet one analyst said: "Putin would not co-operate without something in return." That might include a greater voice in international security, membership of the World Trade Organisation, concessions on Nato's eastern expansion, or compensation for a reduction in Russian arms sales to US-dubbed "rogue states".

In exchange, Russia is set further to sacrifice the influence in Central Asia it enjoyed through the Soviet period.