IN a rare admission of internal friction, the leading state environmentalist in China has disclosed opposition to the construction of the world's largest dam.But Qu Geping, director of the State Environmental Protection Bureau, stopped short of condemning the proposal to build the massive structure at the Three Gorges on the Yangtze River. "Many environmental protection experts ... are firmly opposed" to the dam, Mr. Qu said at a Dec. 4 press conference. They believe "feasibility studies had not been adequately conducted and that great disasters could result from the project." Amid a rising chorus of official support for the $10.8 billion structure, Qu's comments sound a lone note of disapproval. Official newspapers and magazines in the past several months have hailed the hydroelectric dam as a flawless answer to the energy shortage and threat of floods in central China. Advocates of the dam say it will spur trade on the upper reaches of the Yangtze, generate 17,680 megawatts of electricity, and harness the flooding that has regularly ravaged the Yangtze basin over the past several hundred years. These arguments contrast with outspoken criticism of the dam in early 1989. Critics of the dam contend that China can more cheaply control floods and enhance its hydroelectric production by building several smaller dams on the Yangtze's tributaries. The "dam busters" note that the structure would not yield any revenue until halfway through its 18-year construction period. It would cause severe environmental damage and harm some 1.1 million people who would have to move to make way for the dam and its reservoir, they say. The crackdown against pro-democracy activists in June 1989 ended the public debate on the dam and marked a comeback for conservative leaders. Since then, orthodox socialist planners have tried to rally the state behind the titanic structure. The conservatives justify the terrific financial, social, and environmental costs by saying the dam would have prevented the severe floods last summer, which killed more than 3,000 people. Critics of the dam say the floods would have been far less damaging if the state had adequately maintained dikes and instituted sound evacuation procedures. Political leaders who are considered more pragmatic have recently spoken in favor of the dam. Wan Li, chairman of China's rubber-stamp parliament, called in August for an early start-up of the structure. Mr. Wan's endorsement was a major setback for opponents to the dam, Western diplomats say. Moreover, the Communist Party, in a communique released Nov. 29 after a Central Committee meeting, pledged to "speed up the comprehensive control of large rivers and lakes," according to the New China News Agency. Qu noted that the dam would ruin scenic spots, cause severe soil erosion, and harm fish and other wildlife in the Yangtze basin. But he blunted his criticism by commenting on the benefits of the dam in flood control and energy generation. Qu declined to say how the dam builders would ensure the livelihood of millions of poor farmers and fishermen who live below the dam site. The dam would disrupt the seasonal rise and fall of the river, which is critical to the subsistence of the farmers and fishermen, critics say.