YICHANG, China -- Viewed from a boat in the center of the Yangtze, the construction work on the banks of the great river appears massive and urgent.


On the south bank, giant earthmovers clear the path for the diversion channel that will carry the river's flow and boat traffic while the Three Gorges Dam is being built.


On the north bank, workers dynamite canyon-sized grooves in hillsides, building a stepladder of massive locks that will allow seagoing ships to climb over mountains on their way into central China.


If completed as planned, the 200-meter-high, $20 billion Three Gorges Dam would be the biggest hydroelectric project ever built. Communist leaders trumpet the dam as China's biggest public works effort since the Great Wall.


After nearly 70 years of national dreams and discussion -- including a rare, bitter public debate in the National People's Congress -- Chinese Premier Li Peng traveled to the construction site at Sandouping, 12 kilometers east of Yichang, to officially launch the dam project in December.


Since then, the project's 18,000 workers have toiled night and day. At night, headlights from convoys of trucks form a ribbon of light on both sides of the river.


The underlying reason for the urgency is the failing health of 90-year-old senior leader Deng Xiaoping. Despite approval by the National People's Congress in 1992, the project's future is still subject to bitter divisions of opinion among Chinese leaders. Strongly identified with Li, a Soviet-trained hydraulic engineer and leader of the hardline faction in the Communist Party, the Three Gorges Dam is likely to become a political issue again in the post-Deng era.


The dam's builders, working at a furious rate, want as much of a head start as possible before the political succession battle begins following Deng's death.


Hoping to have the first phase of the project completed by 1997, to coincide with the return of British Hong Kong to the Chinese mainland, the engineers jumped the gun on the project start date by more than a year, infuriating the dam's opponents.


"I don't care how much work has been done, the fight over the Three Gorges Dam is not over yet," vowed a retired senior official who maintains a strong interest in the project.


Li acknowledged the political challenges to the project when he spoke at the dam dedication. Standing on a sandbag stage overlooking a construction pit, he pledged that with the support of the Communist Party central leadership, "no difficulty will beat us. ... By 2009 [the project's completion date], a magnificent Three Gorges project will stand rock solid in the great land of China."


Since the beginning of the century, some Chinese have dreamed of damming the Yangtze downriver from the 120-mile stretch of steep, narrow canyons known as the Three Gorges to produce electricity and control flooding. It was first proposed as a national project by Sun Yat-sen, the founder of modern China, in 1920.


Engineers have long been fascinated by the setting's challenge and potential. Dam builders with the U.S. Bureau of Reclamation worked with the Chinese to come up with a design in the 1940s. Soviet engineers arrived to pick up their work in the 1950s.


But despite devastating floods on the lower Yangtze, which have killed 300,000 people in this century, the idea of damming the river the Chinese call "the Great" has never been without fierce opposition here.


The project is opposed by environmentalists inside and outside China who argue that the dam will flood one of the world's great natural sites, destroy habitats of rare species such as the giant Chinese river sturgeon and obliterate cultural landmarks dating to the legendary era of the Three Kingdoms (circa A.D. 200). The feasibility of resettling 1.2 million people who live in 13 cities and towns that would be flooded has also been questioned.


But the dam's planners insist that the project will be built as designed. "There is no turning back," Lu Youmei, general manager of the Three Gorges Development Corp., said in an interview in his Hubei province headquarters in Yi-chang. "The Chinese government is determined to build the dam."


In the end, it may be economic rather than environmental and political factors that make the difference in the future of the Three Gorges Dam. China admits that it has at least a $3 billion shortfall in financing the dam.