But he was careful to insert the qualification that the Government had 'no immediate plans' to go beyond current consideration of the possibility of a call to stop repeated Serbian infringement of the United Nation's no-fly zone over Bosnia.
The Prime Minister's considered response to growing pressure for intervention prompted Paddy Ashdown, the Liberal Democrat leader, to deliver a fierce attack on the Government last night.
He accused Mr Major of washing his hands of Bosnian atrocities; said British policy was 'spineless' in the face of Serbian 'cowards'; and warned that the only hope left was that public revulsion against the horrors to come would overwhelm the politicians' complacency.
Following discussions on Wednesday between Douglas Hurd, the Foreign Secretary, and Malcolm Rifkind, Secretary of State for Defence, both ministers yesterday presented a cautious line before, during and after yesterday's Cabinet.
That line was firmly restated during Prime Minister's questions when Mr Ashdown warned that time was running out for saving lives and stopping the spread of the conflict.
Mr Major replied: 'Those who talk glibly about bombing from the air really should consider the risk of retaliation to our own troops, there at present, delivering humanitarian aid.
'Those who go further, and talk about putting ground forces in, should realise that, were we to do so, we would be committing them to a very long and very bloody fight with the absolute certainty of serious causualties.'
To a cheer of support from his own benches, he added: 'If we have not put in troops, it is not done out of neglect, it is out of our judgement of what is best, what is feasible, and what is responsible.'
Earlier, in an interview on BBC radio, Mr Rifkind repeated that a distinction had to be drawn between a military response to invasion of a country, as in the Falklands and Kuwait, and civil war - where intervention could require tens of thousands of troops, with no guarantee of success.
Mr Ashdown said last night that he was not suggesting that there was a military solution, but he added: 'A political solution is not possible while the Serbs keep on taking Bosnian territory and slaughtering Muslims.
'The massive misjudgement the Government is making is that these people are not the IRA, they are not the Vietnamese; I've watched these people; they are local town thugs. They are not trained, they are not fit, they are not prepared to close with the enemy. They run whenever someone actually fires back at them; these are cowards, most of them. And they are no longer fighting for their homeland.'
Mr Ashdown said that while Bosnia 'burned', the conflict could not be stopped at Kosovo, Macedonia or other parts of the region. 'Nobody does that calculation. We hear always the calculation of action. Nobody has calculated the cost of inaction.'Reuse content