THE British Army is to begin its withdrawal from the territory next month with the disbanding of the Saracen troop which forms part of the Gurkha Transport Regiment. The Saracen troop will be the first to leave this year followed by a reduction in the number of British Army Scout helicopters and the withdrawal of the last Hongkong-based honour guard from Korea, where it has been stationed for more than 40 years. An ongoing review of the pace of military withdrawal will also decide whether the Black Watch, which took over from the Royal Regiment of Wales last month, will be replaced when its tour ends in 1995. The Deputy Commander British Forces, Brigadier Christopher Hammerbeck, said last week the Saracen soldiers and their 40 armoured vehicles would be disbanded next month. ''They'll actually cease to be operational from March 31 and we're awaiting a decision on what should be done with the vehicles,'' said Brigadier Hammerbeck. ''It's an elderly armoured vehicle that no longer meets our needs.'' The 45-strong troop, made up of a seconded British officer and Gurkha soldiers, will be posted in Britain later this year and followed soon after by members of the supporting units which maintain the vehicles. Thirty of the Saracens sent to Hongkong in 1975 are based at the Gun Club Hill Barracks with another 10 armoured cars kept in reserve at Blackdown Barracks. Brigadier Hammerbeck said the vehicles could be used as targets on Castle Peak ranges. Other options being considered include passing the armoured cars on to museums or selling them to another country or Hongkong departments. According to the brigadier, the scale and rate of reducing the number of Scout helicopters in Hongkong had not been decided. There are eight Scouts in Hongkong. Meanwhile, the Hongkong-based United Nations honour guard will also leave Korea next month and return to duties in the territory. The British Secretary of State for Defence, Mr Archie Hamilton, said the platoon would be withdrawn by March 15.