The family of a young South Korean who disappeared after saying he was leaving the United States on a trip to Europe has charged that he is not a defector but was abducted and taken to North Korea by force.

North Korea has produced Lee Jae Hwan, 25, the son of a South Korean legislator, on radio and television, and he has said he went to North Korea voluntarily because of disillusionment with South Korea and capitalism.

Lee, a doctoral student at Massachusetts Institute of Technology, disappeared July 20. He had returned from a three-month tour of Europe on July 17, and after staying with an uncle in New Jersey for three days he left again, saying he wanted to attend a concert in Vienna. His family has not heard from him since.

Rep. Lee Young Wook, a legislator and member of South Korea's ruling party, said in an interview last night in Seoul that he is certain his son was kidnaped and did not defect. Family and friends say that Lee Jae Hwan was not involved in politics and rarely mentioned North Korea. They said that they can see no reason for someone from a wealthy, prominent family, with a future in business, to move to North Korea. Lee was studying economics and management science at MIT.

Lee appeared on North Korean television Wednesday, saying he had defected because he was disillusioned with South Korea and capitalism. During an interview on North Korean radio Sunday he had put it this way: "I was disillusioned with the South Korean society, a colony where everything has been sacrificed for the outside forces, and with the capitalist world, where corruption and immorality prevail."

A State Department official said the department is looking into the possibility that Lee was kidnaped. "We are concerned," he said. "We want to be as helpful as possible."

A member of Lee's family quoted him as saying he was returning to Europe because during his first trip, a group tour with other college students, he had not had enough chance to pursue his own interests, particularly music. He reportedly said he would return to the United States after a few days.

If Lee was not abducted, and did not plan to defect, it is possible that Lee was duped into going to North Korea, naively thinking he would later be free to leave, a knowledgeable source in Washington said. Although there have been previous allegations by South Korea of abductions to the North, recent conciliatory moves by North Korea, such as an offer this month to resume discussions with the South, make abduction seem less plausible, the source said.

The South Korean Foreign Ministry attacked North Korea earlier this week for what it called "savage-like abduction activity."

Rep. Lee and Foreign Ministry spokesman Kim Hang Kyung both said that if the younger Lee did defect, the North Koreans should allow him to be interviewed by a neutral party in Geneva or the Korean truce village of Panmunjom.Washington Post correspondent Fred Hiatt in Seoul contributed to this story.