TWO Hong Kong women were convicted of drug smuggling by Singapore's High Court yesterday and one of them was sentenced to death. The death sentence, mandatory in Singapore for anyone trafficking in more than 15 grams of heroin, was imposed on 21-year-old Poon Yuen-chung. Her companion, Lam Hoi-ka, 19, was sentenced to life imprisonment. She escaped the capital penalty because she was under 18 at the time of the offence. Mr Justice Mohidin Rubin called on all those present in court to stand before telling Poon: ''The sentence on you is that you be taken from here to a place of execution to be hanged.'' She stared blankly at him and showed no signs of emotion. When Poon and Lam were arrested at Changi Airport in July 1991, after flying in from Bangkok, the women, aged 17 and 19 at the time, were described by customs officer as ''trying to look like schoolgirls on holiday''. The women, who have spent the past two years in prison, were charged with importing between them a total of 6.52 kilograms of heroin. The death penalty is subject to an automatic appeal in Singapore. Lam could be held indefinitely. The law provides that a person under 18 who is convicted of a capital drug offence will be detained at a place directed by the President until such time as he decides she should be released. Deputy Public Prosecutor Ong Hian Sung told the court that Poon and Lam, who were described as sales assistants, were stopped by an officer at the customs counter on the morning of July 16, 1991. When the officer saw from their passports that they had arrived from Bangkok, he searched Poon's bag. Suspecting it had a false bottom, he asked the women to go to the Customs Duty Office. There officers found slabs of heroin concealed in false bottoms of both women's bags. The officers found 12 blocks and a packet of heroin in Lam's bag. They were later tested and found to comprise 3.46 kilograms of heroin. The prosecutor said Poon's bag contained 3.06 kilograms of heroin. The heroin was said to be worth S$9 million (about HK$44 million). Both women, who were provided with lawyers by the state, denied knowledge of the drug. They claimed that they had met a Chinese couple in Bangkok who took them out for dinners and sightseeing tours. The couple then bought suitcases for them and transferred their belongings from their old suitcases into the new ones. Poon and Lam had said in their defence that they did not suspect anything about the bags until their arrival in Singapore when customs officers checked them and found the drugs. Two Hong Kong men were executed by hanging for drug offences in July and a man and woman from the territory face the same fate after being sentenced to death in another drug case last month. Singapore has executed 42 people since the mandatory death sentence for importing or possessing heroin was introduced in 1975. Another 40 people, including the Hong Kong pair, are either awaiting trial or appeals against death sentences for drug offences.