In their ruined homeland, returning families will find another 500,000 homeless compatriots living in a state of semi-starvation - foraging for food in the hills.
An acute food shortage is worsening. Only a third of Kosovo's agricultural land was planted in the spring before the war began. Most crops have not been gathered and have withered. Much of the livestock has been slaughtered - many animals stolen by Serb soldiers - or has died of hunger. There is neither fertiliser nor pesticides. The water supply is contaminated and there is little power.
"At least we know where we stand," said Abby Spring, of World Food Aid, the organisation that will co-ordinate the distribution of international food relief inside Kosovo.
"We've been preparing for this and we are ready to go in tomorrow if necessary, just as we will be prepared to go in next week, or the week after that."
At present, UN food officials have enough supplies stockpiled to look after every refugee for a month. But once you add on the number of internally displaced people, the figure is nearer two weeks. The stockpile is growing by the day and a fleet of lorries is on standby to deliver it.
Meanwhile, staff of the UN High Commissioner for Refugees are holding regular co-ordinating meetings with Nato and agencies involved in providing food, medicine and clothing. The main problem is the logistical one of getting the supplies to those in need. Bridges have been blown up, roads mined and buildings booby-trapped by the Serbs. In addition, there is the damage caused by Nato air strikes.
The plan is for the refugees and the humanitarian aid to start moving when the peacekeeping force for Kosovo says it is safe to do so. But military and aid officials know that it will be impossible to stop groups of Kosovars from moving across the border from Macedonia and Albania once the Serbian withdrawal starts.
Many will travel home in their tractors - one of the few possessions they managed to flee with. These might be vulnerable to anti-tank mines laid by the Serbs. The wounded will have to be treated by army doctors or those from medical charities.
When UN refugee officials and the aid agencies do go into Kosovo, a priority will be to track down the vast numbers of internally displaced people as soon as possible. Helicopters will be used for these search missions and, if necessary, to drop food and other essentials.
The headquarters for the humanitarian mission will be in Pristina, the Kosovo capital. But mobile warehouses will also move around the land, and a series of regional centres will be established.
One of their roles will be to help to reunite refugee families who were separated when they fled the province.
Nato forces will try to ensure that returning refugees are not attacked by Serbian irregulars, who may still be lurking. The countryside around the main routes to be used by the refugee convoys of cars and lorries, as well as the rail lines, will be searched to flush out snipers.
Western armed forces are expected to play a role in the humanitarian effort by helping to move supplies, putting up temporary accommodation and providing clean water.
Officials are concerned about the danger of clashes among refugees.
Fears of such trouble have grown since an attack on a gypsy family in Macedonia's Stankovic 1 camp on Saturday. A mob of Kosovars attacked them with clubs, accusing them of looting their homes in Kosovo.
The humanitarian operation is a hugely costly business, despite the assistance from various countries. So far, $63m has been spent on feeding the 800,000 refugees in camps in Macedonia and Albania. Estimates say 15,000 tonnes of food will be needed to sustain the population in Kosovo for the initial period.
Abby Spring said: "We aim to make sure every returning refugee has up to three days of high-protein food when they head back. We'll also ensure they pick up food on the way which should last them about a month.
"This is certainly one of the most difficult and complicated tasks we've ever undertaken."Reuse content