BEIRUT, OCT. 28 -- A South Korean diplomat held hostage since January 1986 has been released in return for $1 million in ransom, Nabih Berri, Lebanon's justice minister and leader of the Shiite Moslem Amal movement, said today.

Berri, at a news conference, said Amal security forces had helped in ensuring Do Chai Sung, 38, a second secretary at the South Korean Embassy here, safe passage out of Beirut. He flew to Seoul yesterday.

"Regretfully, and according to my information, not less than $1 million was paid for the release of the South Korean diplomat," Berri said. He and other officials did not indicate who had paid the ransom.

Amal helped negotiate an end to the TWA hijacking in 1985 and other kidnapings here. Berri refused to identify the kidnapers and said Amal only facilitated Do's departure. "Yes, Amal protected him after his release, but we had no role in freeing him," Berri said.

The previously unknown Green Brigades claimed responsibility for Do's seizure and demanded a $10 million ransom.

The Lebanese Broadcasting Corp., a television station run by the Christian Lebanese Forces militia, broke the news of Do's release. When asked how it learned of the release, a station official said, "Just ask the Syrians." About 7,000 Syrian troops were deployed in mainly Moslem west Beirut last February.