Stung by years of humiliation, members of South Korea's major opposition party are rebelling against their leader for being too closely associated with President Park Chung Hee.

New Democratic Party chairman Lee Chul Seung, 54, is under severe pressure to resign after facing a seven-hour barrage of taunts and angry questioning at a party caucus yesterday. He was attacked for making statements sympathetic to the authoritarian Park government during a just-concluded tour of the United States and Japan.

Sources who attended the closed-door meeting in the party's shabby headquarters say, however, that it became a bitter quarrel over the party's ineffectuality.

The debate is as much a search for party survival as a struggle for leadership. Legislated and manipulated into impotency over the last five years, the New Democrats face a difficult election in two years and need a formula to attract voters.

"They are losing their prestige and their constituency," said a Western political analyst. "They're worried it could lead to their extinction."

The party's fortunes have steadily declined since Park took power in a 1961 military coup. In 1972 he declared martial law, dissolved the National Assembly and imposed a new constitution that made the president the supreme authority, downgraded the National powerless.

The New Democrats have 55 members in the 219-seat assembly where Park's Republican Democratic Party and another group appointed by him always holds the majority.

Since Lee took over the National Democratic leadership last September, the demoralized and dissension-ridden organization has tried to expand its Assembly role by cooperating with Park's party. The members had to reassess this approach this week when the Supreme Court upheld the conviction of new Democratic stalwart Chung II Hyung on political charges and stripped him of the seat he had held since 1950.

Chung's fate and his farewell speech before yesterday's caucus shocked and shamed many of his colleagues into a combative mood. The one-time foreign minister said it was a relief to have the National Assembly and end the humiliation he had felt there.

The caucus gave him a standing ovation. It closed by adopting a statement seeking rehabilitation of the party's image and reversal of the Supreme Court verdict on Chung. It also demanded that the Assembly be convened in special session to debate the case and "important international issues." The latter is an apparent reference to U.S. plans to withdraw ground forces from Korea.