THE actual role of the Black Watch regiment in Hongkong was now limited and its troops were far more dispensable than other units based here, senior defence sources said yesterday. In theory, the 600-soldier infantry regiment ''demonstrated British sovereignty and protected the internal and external integrity of Hongkong'' but in reality any threats to either were considered exceptionally slight. ''They are here basically for training, just to keep battle-ready and much of that is done overseas,'' one officer said. ''In terms of what they mean for Hongkong, other assets are far more valuable with the navy chasing smugglers and the Royal Air Force staging rescues.'' The role of the Black Watch is believed to be a factor in the review of the 7,000-strong British Garrison. Reports from London now suggest the Black Watch - tipped to be the last British regiment to serve in Hongkong - will withdraw next year instead of 1995. Together with the 10th Gurkha Rifles and the 2nd Gurkha Rifles, the Black Watch form a 1,800-strong band of infantrymen. The report has yet to be confirmed officially by British Forces Hongkong or the Hongkong Government but both say a statement on the phased withdrawal in the run-up to 1997 is just weeks away. When asked if there was a pressing need for the Black Watch to stay in Hongkong, a Security Branch spokesman said: ''If there was a pressing need for them to stay there would not be the need for such a review. ''Whatever the decision, there will be no vacuum in terms of what's needed for Hongkong.'' One company of about 150 men has just returned from Hawaii after training with US Marines while two others will leave shortly on similar stints in Malaysia and New Zealand. Joint Forces spokesman Arthur Murray said it would only be in ''exceptional circumstances'' that Governor Chris Patten would call on the infantry soldiers to quash internal crises as Commander-in-Chief of the British Forces Hongkong. Threats to external security were considered low. ''The internal security role has now been passed on to police and there is much less of an anti-II role,'' Mr Murray said. ''They do have to spend a lot of their time training.'' However, Gurkha transport, engineer and signals regiments provided skills and equipment vital in civil disasters, he said. The imminent announcement from the Commander British Forces in Hongkong, Major-General John Foley, would also deal with the question of what would happen to defence lands in Hongkong vacated by the military before 1997. Mr Murray said the British Forces had no intention of holding sites leased from the Hongkong Government if they were surplus to requirements as withdrawals took effect. The Black Watch currently occupies Stanley Fort, which includes a primary school and sports ground used by other military personnel. The Sino-British Joint Liaison Group has not yet resolved the disposal of military sites after 1997.