Most, if not all, are Jehovah's Witnesses, a Christian group that has been a niggling thorn in the side of the authorities for more than 30 years. Its members say donning a military uniform runs counter to their strongly held beliefs, which do not permit ''taking up the sword''. The government says their refusal is ''disruptive of the national ethos'' and indicates it is prepared to go on jailing those refusing to serve.

The curious showdown has drawn little in the way of public attention, either locally or from foreign media. Singapore is better known for its hard-earned efficiency and well-honed pragmatism than as a place that regularly puts dissidents into military detention.

But the treatment of the men - who number just a fraction of those who perform the compulsory service each year - highlights a yawning divide between Singapore's rulers and human-rights campaigners. While the government stresses the interests of the many over the needs of the few, the activists charge that individual beliefs must be respected.

Those serving time have said that when forced to choose between remaining true to their beliefs and losing their freedom, or yielding to the directives of the state, they feel there is only one course of action open to them. ''I am just doing what Jehovah requires me to do,'' one of the accused told an Australian newspaper at his court martial in the late 1990s. ''It's very plain in the Bible.''

National service has been a key part of Singapore's defensive posture for decades and buttresses the ability of a population-scarce country to repel potential aggressors. The male draftees - women are exempt - are obliged to devote between two and 2 years when they turn 18 to mastering the basics of military skills. Annual refresher courses are also required for ''operationally ready national servicemen'' until they are 40. No ''soft'' non-military alternative is offered.

Getting a society traditionally unused to the practice of military service to accept the policy was no easy task. It required ''social engineering'', said S. Dhanabalan, a former minister and current head of Temasek, a government holding company.

Lee Kuan Yew, former prime minister and now Senior Minister, said that the months spent in the forces had become ''a rite of passage for our young men and part of our way of life''.

The elder statesman contends in his memoirs that the practice is both respectful of ''all religious rites'' and helps to reinforce the city-state's strong focus on meritocracy. ''Whether your father is a minister, banker, professional, taxi driver or hawker, your military standing depends on your performance,'' he said.

And on the whole, that message has been accepted, with most young Singaporeans and their parents apparently supportive of military service.

Jehovah's Witnesses have not seen it that way, setting them on a collision course with Mr Lee, Prime Minister Goh Chok Tong and their fellow ministers.

Followers - who are thought to number between 1500 and 2000 - have periodic skirmishes with the government over their refusal to sing the national anthem or recite the national pledge. But it is the national service issue that has been the main source of friction.

The government acted in 1972, banning the Singapore Convention of Jehovah's Witnesses (SCJW), but claiming at the time and subsequently that the ban did not in itself undermine a person's freedom of belief.

An official from the Ministry of Defence explains the legal reasoning. ''It is only an offence to be a member of the SCJW. It is, therefore, not illegal to profess the beliefs of the Jehovah's Witnesses per se, nor is it an offence to be a Jehovah's Witness,'' she said. ''It is the manner of carrying out these activities that is circumscribed by the relevant legislation.''

One of the more forceful explanations of the official position came in a ruling from Chief Justice Yong Pung How when dismissing an appeal by four Jehovah's Witnesses who had been convicted of possessing banned SCJW literature.

''Any organisation whose members are bound by its own rules not to do national service, whether it be Jehovah's Witnesses or a mere society to promote the playing of tiddlywinks or something else, must have to face de-registration,'' he said. A failure to act would allow the group to become ''an easy refuge for people who wish to evade national service'', he said.

The stance angers human-rights groups, including London-based Amnesty International, which regularly calls for the Singaporean detainees to be freedwithout conditions.

''Amnesty believes the imprisoned Jehovah's Witnesses to be prisoners of conscience,'' a spokeswoman said. ''They have been detained for their refusal on religious grounds to perform military service.'' For the campaigners the crux is not one of endorsing the Jehovah's Witnesses' particular beliefs, nor of disputing the right of a sovereign government to call up its young men to serve in the military. It is about choice.

''In keeping with international standards, Amnesty International insists that all those liable to conscription be given the opportunity to perform a genuinely civilian alternative to service in the armed forces on the grounds of their conscience or profound conviction,'' she said.

Given that the government refuses even to recognise ''conscientious objection'' the standoff is likely to last far into the future. And in the years ahead there will continue to be young men who contemplate their life and beliefs from the confines of a military prison.