The sharp drop in support revealed by today's Guardian/ICM poll confirms Tony Blair's fears that the reality of modern warfare and reports of mounting civilian casualties have already led to a wobble in British support.

It provides clear evidence that there has been a significant change in the mood of the country towards the war and explains why ministers have spent the last weekend trying to shore up public opinion and why the prime minister is to appeal to the nation to "keep its nerve" in a major speech today.

Although the prime minister will take comfort from the fact that nearly two-thirds say they approve of military action, the prime minister will be alarmed by details of the survey, which show that support among women has slumped by 17 points from 68% to 51%. Only a bare majority of women now approve of military action against the Taliban.

It is a similar picture among older voters, with support among the over 65s dropping from 71% to just 54% in the past fortnight. The slide in support for military action is least marked amongst men, where backing for the war has fallen by only six points from 80% to 74%, and among the young, down from 73% to 64%.

But it should be noted that while positive support for the war has cooled somewhat, this has not necessarily translated into anti-war feeling.

Those opposed to military action have risen by only four points in the last fortnight from 16% to 20%. The largest growth has been among humanitarian sceptics, with don't knows rising by eight points to 18%.

This is shown most clearly by the clear majority who agree with the statement that there should be a pause in the bombing campaign against the Taliban to allow aid convoys to go into Afghanistan.

A majority of 54% believe this should happen, with 29% saying that the bombing campaign should continue without pause.

When viewed against the 62% support for military action, this suggests that the clear motive behind those who back the calls for a pause in the bombing is humanitarian rather than outright anti-war reasons.

Among women there is overwhelming support for a pause (59% to 19%) but opinion among men is closer, with 49% in favour of a pause and 40% opposed.

Further evidence that it is a humanitarian inspired wobble in public opinion rather than outright opposition to the war is shown by the results to the question on attitudes towards sending British troops into Afghanistan to take part in the fighting on the ground. Some 57% backed the decision announced on Friday for a small force of British commandos to be sent to Afghanistan.

Some 29% disapproved of this decision, showing that there is only a small gap in British public opinion between attitudes to the bombing campaign and to use of British troops on the grounds.

A final question about public confidence in the government's ability to deal with a major outbreak of anthrax, smallpox or other public health threat, produced mixed results. A substantial minority, 44%, replied they were either not very confident (29%) or not at all confident (15%) that the government could cope.

A bare majority, 51%, said they were either very confident (12%) or fairly confident (39%) that the authorities could deal with it effectively.

· ICM interviewed a random sample of 1,000 adults aged over 18 by telephone between October 26 and 28. Interviews were conducted across the country and the results have been weighted to the profile of all adults.

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