Mr Robertson announced plans to cut Britain's reserve armed forces by a third, closing drill halls across the country and saving taxpayers pounds 100m.
He said the Territorial Army would be turned into a front-line force, which would be trained, for the first time, on the Challenger 2 main battle tank and heavy guns.
Despite the plan to reduce the TA from 54,000 troops to 41,200, a recruitment drive is to be launched, with television and cinema advertising to attract more young people,
For the first time, reservists could be compelled to serve abroad if there was a crisis like the Gulf War. That conflict highlighted the need for the change in the TA's role: Tory defence staff discovered that the reservists were legally engaged to defend the UK, but not to fight abroad.
Mr Robertson told MPs yesterday: "The Government will be prepared to call up the TA in formed units if need be in situations short of direct threat to the UK itself, like the Gulf War. What we are proposing is a radical shift away from the TA's traditional image as 'weekend warriors' towards a new, more heavyweight role in the world after the Cold War."
The law was changed in 1996 to allow the army to supplement its forces abroad with reservists. TA reservists already serve in Bosnia, on the green line in Cyprus and in Northern Ireland. But the drive to a more modern, mobile force, backed by the chiefs-of-staff, is likely to increase pressure on reserves to serve on the front line in peacekeeping missions.
Most of the cuts will fall on the TA infantry, which will be reduced from 33 battalions to 15. The number of armoured corps will be cut from seven to four, logistic corps will be cut from 19 to 14 regiments and the TA bands will be reduced from 24 to 14. But the reserve medical forces - which were vital in the Gulf - will be increased by 2,000 men, the two SAS regiments of TA will be retained, and force equipped for dealing with nuclear, biological or chemical warfare will be doubled to two units.
Critics said the "brass hats" at the Ministry of Defence, out of snobbery towards civilians serving alongside full-time soldiers, had tried to cut the TA under the Tories but had been unsuccessful. Now they had finally got their way.
Julian Brazier, the Tory MP and a former TA captain, accused the Defence Secretary of using "smoke and mirrors". He said the reserves would never be able to use the tanks, because there were none sparefor training.
"It's very misleading to suggest that they can have a few days on tanks on Salisbury Plain. It's a complete disaster," he said.
Mr Robertson blunted much of the criticism by reprieving TA units in Scotland after heavy lobbying by Donald Dewar, the Scottish Secretary.
The briefing room at the Ministry of Defence in Whitehall used to announce the changes to the TA yesterday had been secretly earmarked for press conferences on the attack onIraq if the air raids had gone ahead at the weekend, it was revealed yesterday.