PLANS to close Tai A Chau, one of Hong Kong's 'Big Three' Vietnamese detention centres, by the end of next month have been delayed indefinitely. Operating costs for the camp are more than $1 million a week. Hopes of meeting an internationally set deadline for closing all the camps by the end of next year have been dismissed as impossible, but the Government may eventually recoup some of the costs by putting the camps up for sale. The biggest of the camps, Whitehead detention centre in Sha Tin, is considered prime real estate with its 50-hectare Tolo Harbour site. Some savings in the Vietnamese programme will also be made from December 1 when the tough island prison of Chi Ma Wan (Upper) becomes a women's prison run by the Correctional Services Department. Almost 24,000 Vietnamese boat people remain in Hong Kong of the approximately 200,000 who have arrived since 1975, but the cost of supplying staff and feeding the camp population has been huge. In the coming months, the programme will begin to wind down and substantial savings will be made, though millions of dollars owed by the United Nations High Commissioner for Refugees (UNHCR) will never be recovered. A government spokesman said the food bill for last year in Vietnamese camps run by the Correctional Services Department was $107 million and, for this year, $51 million had been spent to the end of September. In theory, these and other costs are to be borne by the UNHCR, but because of a lack of funds, the Government pays and as a matter of course adds the payments to the UNHCR's tab. The UNHCR owes Hong Kong more than $1 billion - an amount the Government concedes it is unlikely to receive because of demands on the UN elsewhere in the world. A Government spokesman was unable to say what the future of the Tai A Chau camp was with its remaining population of 6,421. However, it has previously said it had hoped to clear the camp by the end of the year by moving the remaining detainees to the High Island detention centre - home to more than 2,300 southerners. The budget for the Tai A Chau camp for 1994/95 is about $55 million, excluding food and relief items. Unlike the other detention centres, Tai A Chau is administered by Hong Kong Housing Services for Refugees at the request of the UNHCR. A spokesman for the service said he had no knowledge of when the camp would be closed down or what would become of it. Delays in closing the camps have been brought on by a reluctance in the Vietnamese to volunteer for repatriation. At the height of Vietnamese arrivals, about 20 camps and halfway houses were operated. A Lands Department spokesman said no thought had been given to what would happen to the Whitehead and High Island camps. He said High Island was a unique case because it was in the Sai Kung Country Park and it would be difficult to use it for anything else. He said Whitehead would probably be used for low-density residential or recreational development.