SINGAPORE -- Sitting in his spartan room on a small island just off this city-state's main waterfront, Chia Thye Poh does not look like much of a security threat.

Soft-spoken and unassuming, he seems to devote considerable time to keeping his quarters meticulously tidy. Tourists occasionally wander into Chia's room, obliging him to explain what he is doing there as the island's only permanent inhabitant.

But the mild-mannered former physics teacher is regarded as an enemy of the state by a formidable adversary -- Lee Kuan Yew. Chia serves as a reminder that there is another side to the story of Lee, who resigned last month amid lofty accolades as the world's longest-serving prime minister but still wields considerable power here.

Until his release last year, Chia had spent 23 years -- nearly half his life -- in Lee's jails, making him one of the world's longest-held political prisoners.

Now he is under a loose form of house arrest on Sentosa Island, where he occupies a former Gurkha guardhouse in the century-old Fort Siloso. It is an unusual form of internal exile. Sentosa, described in government tourist literature as a "scenic, fun-packed discovery island," is a one-square-mile amusement park, Singapore's version of Disneyland, and the former British colonial fort is one of its main attractions.

Singapore is not considered a major human-rights violator, although the government has exercised strict control over many aspects of life. Under Lee, Singapore became prosperous, but his ruling People's Action Party has defied the trend of democratization in other countries, trying to assert control over the local and foreign press and moving to intimidate the opposition.

Chia's case exemplifies what the human-rights group Asia Watch calls the "potential for severe abuse" of the country's Internal Security Act, which permits indefinite detention without trial. It also illustrates Lee's political vindictiveness, a trait that some of his countrymen feel tarnishes his image as the builder of modern Singapore.

To date, Chia, 49, has never been tried, or even formally charged with a crime. A former opposition member of parliament from the leftist Barisan Socialis party, he was arrested under the Internal Security Act in October 1966 at age 25.

Although the government says the last political prisoner held under the act was freed in June, Chia still considers himself a detainee. His release, he insists, should be unconditional.

"My main concern is my complete freedom," he said in an interview in his sparsely furnished, concrete-floored room. "I'm still a prisoner here."

Whether by coincidence or design, Singapore's Internal Security Department issued Chia a new "restriction order" effective for two years from Nov. 28, the date of Lee's resignation as prime minister after 31 years in office. Lee has insisted that the Internal Security Act, under which hundreds of political offenders have been jailed since the 1960s, is still needed to control "extremists" and that Singapore "has always to be a tight ship."

Pointing out that Lee remains in the cabinet as a "senior minister," Chia said he sees "no real relaxation yet" of political controls. "So far, we are still under one-party rule," he said.

The new Internal Security Department order for Chia says "certain restrictions" must be imposed on him to prevent him "from acting in any manner prejudicial to the security of Singapore."

He must reside in the guardhouse and remain on Sentosa between 9 p.m. and 6 a.m. He is allowed to visit the main island during the day and take a job there, provided he obtains "prior written approval" from the Internal Security Department. He may not leave Singapore without such approval or associate with any political dissidents. He may not issue public statements, address public meetings, participate in any political organization or "take part in any political activity" without approval.

Still, Chia said, "politics is in my blood." Indeed, he and Lee seem locked in a test of wills that shows no sign of ending.

Chia was arrested after he quit the legislature with nine Barisan Socialis colleagues, vowing an "extra-parliamentary struggle" against Lee's government through "street demonstrations, protest meetings {and} strikes."

The first official explanation of the arrest came 19 years later. Home Minister Shanmugam Jayakumar told parliament in 1985 that Chia had been a member of the Communist Party of Malaya under orders to penetrate the Barisan Socialis and engage in "Communist united front activities to destabilize the government."

Chia has called this a "sheer fabrication" and challenged the government to prove it in court. He said authorities privately ruled out any trial but promised to free him if he simply signed a confession admitting membership in the now defunct party and renouncing violence.

"I told them I don't have anything to confess," Chia said. "I have never been a member of any communist party. And I have never advocated violence."

Immediately after his arrest, Chia said, he spent a month in solitary confinement in a dark, filthy cell in the Top Floor Center, a former jail for political detainees. He said he was not physically tortured but was subjected to severe psychological pressure in an attempt to "brainwash" him. Guards told him that inmates there often went insane after several days.

"I thought I might go insane too," he said. "But somehow that did not happen."

Early in his detention, he found a poem written in fine, barely legible handwriting on a cell wall by an unknown inmate. He committed it to memory:

Ten years behind bars

Never too late

Thousands of ordeals

My spirit steeled.

"I thought I should emulate that spirit," Chia said.

His own ordeals followed, he said: Punishment for refusing to do forced labor in what prison officials termed "hobby classes"; a hunger strike that authorities broke up by force-feeding political prisoners through tubes in their nostrils; deteriorating health in a stifling, dimly lit cell in the Whitley Road Holding Center.

"They wanted me to pay a very high price for not kowtowing to them," Chia said.

Now he must deal with the somewhat humiliating experience of being what one U.S. human-rights activist has called an "exile in Disneyland."

Amid theme parks with names such as Nature World, Sun World and Fun World, Sentosa features a monorail, two golf courses, sandy beaches, tropical gardens, a variety of museums and a pair of lagoons with canoes and pedal boats. Other attractions include the "World Insectarium," reputedly one of the planet's largest collections of bugs.

Then there is Fort Siloso, now showing an exhibit called, "Behind Bars -- Life as a POW." The fort, built by the British in the 1880s, was used as a prisoner-of-war camp by the Japanese from 1942 to 1945.

But Chia's surroundings appear to have only hardened his opposition to policies he calls "undemocratic and unjust," including the Internal Security Act and restraints on press freedom.

"In World War II, many people of many races died for the freedom of Singapore," he said. "This place was bombed and turned into a POW camp. When I think of so many people who sacrificed so much, I feel I have a duty to persevere."