SEOUL, NOV. 3 -- Looking frail and exhausted, a South Korean diplomat returned home today after 21 months as a hostage in Lebanon, saying in a trembling voice, "I'd like to forget about the ordeal."

Do Chae Sung, 45, kidnaped by four gunmen in Beirut as he was being driven to work nearly two years ago, had an emotional reunion at the Seoul airport with his wife, children and parents. Foreign Minister Choi Kwang Soo and a horde of reporters were also on hand for the welcoming ceremony, which was broadcast live on the country's main television stations.

"I feel exhausted, physically and mentally, due to my prolonged captivity," Do said at a brief press conference.

Although he declined to go into detail about his detention, Do said he was held in a cell without windows, and did not see any of the more than 20 foreigners kidnaped in Beirut and still held hostage. Do, who says he received only one meal a day, had little contact with other people, was often blindfolded, but was not physically tortured.

"I don't want to recount at this moment how I lived while in captivity," he said in a halting voice. "You can imagine the sufferings of captives, and it is natural for anyone to want to forget the ordeal after being freed."

A great deal of uncertainty still surrounds the kidnaping and release of Do, who was freed last Saturday and then flown to Geneva, where he rested before completing the last leg of his long voyage home. Nabih Berri, the leader of the Shiite Moslem Amal movement in Lebanon who acted as an intermediary in gaining Do's freedom, said at a press conference last week that a ransom of more than $1 million was paid.

The South Korean Foreign Ministry has vehemently denied this, arguing that delicate negotiations involving several middlemen and friendly countries secured the release of Do, a second secretary in Beirut at the time of his kidnaping. "My ministry never paid a penny for his release," said a Foreign Ministry spokesman.

At the time of the kidnaping, a previously unknown group calling itself the Revolutionary Commando Cells claimed responsibility and demanded a ransom of $10 million.

The diplomat said he still does not know who his kidnapers were, why they snatched him off the Beirut streets on Jan. 31, 1986, or how his release was accomplished. The South Korean Foreign Ministry refuses to release details of the case. Foreign journalists were prohibited from attending the airport press conference.