SEOUL, South Korea -- In 1997, when Hwang Jang Yop and Kim Dok Hong defected from North Korea, they were celebrated as heroes here in the South. But by the time Mr. Kim met with South Korean intelligence agents in November 2000, things were very different.

 Days before the meeting, the duo -- the most important defectors ever from the North -- had published the latest in a series of newspaper articles condemning Seoul for muzzling their opinions. Waving a copy of the article, one of the South Korean agents responsible for watching the pair screamed at Mr. Kim, "Do you want me to die because of this?" according to Mr. Kim's assistant, who was there. "If I die, we should die together," the agent said.
   
 Mr. Kim sat unmoved behind his tortoise-shell glasses, then coolly replied, "Fine, let's die together." A senior official with the South's National Intelligence Service says agents have met frequently with Mr. Kim but don't recall this exchange.

 The South Korean government's aggressive campaign to restrain the two turncoats from the totalitarian North offers a revealing window on one of the highest-stakes debates under way in global diplomacy: whether to freeze out North Korea or work with it.
  
 The defector duo spoke with authority when they arrived in Seoul, asserting that the North is a "living hell" incapable of reform. Mr. Hwang, 79 years old and the more eminent member of the pair, served for 17 years as a senior official of the North's ruling Worker's Party. He was also president of the country's most prestigious university and personal tutor to its dictator, Kim Jong Il. Many in South Korea assume that Mr. Hwang and his sidekick possess knowledge that could bring down the northern regime: secrets about nuclear and biological weapons, for example.
  
 What's beyond dispute is that Messrs. Hwang and Kim put themselves sharply at odds with President Kim Dae Jung, a former dissident who campaigned for years to bring democracy to the South. Today, the president is pushing what he calls the Sunshine Policy, a broad program to promote trade, tourism and investment as a way to bring peace to a Korean Peninsula divided for half a century by Cold War.

 U.S. intelligence officials concur that the North is working on nuclear weapons, and the Clinton administration made overtures aimed at persuading Pyongyang to stop. Despite pervasive food shortages, the country channels 25% to 30% of its economic output into developing weapons generally, according to outside experts. Famine killed an estimated one million North Koreans in the early 1990s.

 That crisis might have destabilized the Pyongyang government, but international aid "resuscitated North Korea's regime," Mr. Hwang said in a rare interview last year. "Kim Jong Il was adamant to follow a path of war, even though his people were dying of starvation." There is a broad consensus that North Korea is among the world's most repressive regimes, maintaining n elaborate system of government informants and prison camps for suspected dissidents.
  
 Mr. Hwang, who now has white hair and a hearing aid, spent the 1940s and 1950s mastering Stalinist ideology at universities in Japan and the Soviet Union. He worked his way up to the post of personal clerk to Kim Il Sung, North Korea's tyrannical founder and father of its current supreme leader. The elder Kim, backed by the Soviet army, established the country in 1948, as the formerly united Korea split into pro-Communist and pro-Western camps. In June 1950, Northern troops invaded the South, setting off the three-year Korean War.

 His comrade, Kim Dok Hong, now 63, has worked under Mr. Hwang since the 1960s. Beginning in the 1970s, though, Mr. Hwang said he grew disillusioned with Kim Il Sung's preparing his son, Kim Jong Il, to be the next leader. Mr. Hwang disdained the younger Kim's abilities and opposed the creation of a family dynasty. His revulsion increased as the country's poverty deepened while the regime poured money into the military.

 In early 1997, while traveling through Beijing, the duo made their move. They told their North Korean minders they wanted to shop for a birthday present for dictator Kim Jong Il. Instead, they took a taxi to the South Korean Embassy in Beijing, accompanied by an official from Seoul. To their dismay, the embassy gates were locked, and the South Korean took 10 minutes to find keys. "Those 10 minutes felt like 10 years," recalled Kim Dok Hong. Two months later, they were in Seoul.
  
 From that point on, said Kim Dok Hong and other aides to Mr. Hwang, Seoul moved decisively to silence the defectors. In October 2000, the government shut down a monthly publication on North Korean affairs the two men put out. They lost their positions at a government think tank. And later, NIS officials threatened to toss them out of their government- provided apartments if they didn't stop attacking Kim Jong Il in the press, said Kim Dok Hong.
  
 Conservative American groups, including the Defense Forum Foundation in Falls Church, Va., have been inviting Mr. Hwang to come to the U.S. since 1997, hoping he would describe North Korea's biological- and nuclear-weapons capabilities. Suzanne Scholte, the foundation's president, traveled to Seoul in December 2000, hoping to meet him. South Korean government officials told her Mr. Hwang didn't want to meet her or come to the U.S., as he was working on a book, she recalled. Frustrated, she left Seoul but through the South Korean government passed on to Mr. Hwang a Bible and an open invitation to visit the U.S.
 
 By 2001, GOP Sen. Jesse Helms and Reps. Henry Hyde and Christopher Cox had lent their support to the Defense Forum's invitation. Sen. Helms raised the issue with President Kim Dae Jung when the South's leader visited Washington in March 2001, according to an aide to the senator.

 But Helms staff members found themselves thwarted when they tried to reach Mr. Hwang during a July 2001 visit to Seoul. Three separate meetings with NIS officials failed to produce an interview with the defector.

 Late last year, the NIS hit upon a gambit to block conclusively any Hwang trip to the U.S. The agency played on Mr. Hwang's determination to create a permanent legacy for his version of juche. In a letter to Kim Dok Hong in December, Mr. Hwang wrote that he has only a few years left to complete his life's work on juche and that he wants to create an institute to study and preserve it. The NIS would pay for an institute, and in exchange, Mr. Hwang would abandon his goal of going to Washington, the letter said. "If the U.S. invites me again, I will say I am delaying my trip," he wrote.

 According to a copy of a formal agreement dated Jan. 13 and reviewed by The Wall Street Journal, the NIS has pledged to donate 300 million won ($235,400) for the development of Mr. Hwang's institute in Seoul. The NIS gave him 20 million won as a down payment for construction of a five-story building, according to the document.
  
 At a meeting in January with a representative of Rep. Hyde, the chairman of the House Foreign Affairs Committee, Mr. Hwang signaled he no longer wished to criticize the North. When asked by an NIS agent at the meeting if he still wanted to go to the U.S., according to other people who were there, the defector replied, not if the Americans "want me to explain about nuclear and chemical weapons" in North Korea. The senior NIS official confirmed the meeting and this discussion.

 Mr. Hwang's decision has cost him the admiration of Kim Dok Hong. On Jan. 14, Mr. Kim wrote in a letter to his mentor, "I feel bitter toward you for selling your political honor and conscience for only 20 million won." They haven't talked since.