The US National Guard is planning to cut the number of its troops in Iraq by 75 per cent over the next year in a dramatic change of approach by the American military, The Times has learnt.

The substantial reduction in part-time troops — from eight combat brigades to two — follows growing evidence that the National Guard’s supply of equipment is becoming exhausted, leaving it unable to cope with domestic emergencies, such as Hurricane Katrina.

There has also been speculation that the force is simply running out of troops for deployment and that recruitment is suffering as a result of high casualty rates and unexpectedly long tours of duty in Iraq and Afghanistan.

Guardsmen, who are recruited under the slogan “two weeks a year and one weekend a month”, report to their state governor, not to Washington, and many never expected to fight in foreign wars.

They are permitted to serve only two of their six years abroad. However, many are already on their second tour in Iraq, and there has been widespread concern at the strain being placed on the part-timers, who make up an unprecedented 65,000 of the 159,000 troops in Iraq and have suffered 318 fatalities.

Only 10,000 National Guardsmen served in Vietnam, where about 100 were killed.