(Updates with pollution control measures in paragraphs 7-10)

BEIJING, Nov 21 (Reuters) - A landslide near China's huge Three Gorges Dam trapped four workers, killing one, state media reported, as officials announced efforts to counter environmental fallout from the controversial project.

The landslide hit on Tuesday morning in the central province of Hubei, beside a half-completed railway line near the 660-km (410-mile) dam reservoir, Xinhua news agency reported.

The workers were perched on scaffolding next to a tunnel in Badong County when buried by collapsing earth, the report said. One was killed, another injured and two remained missing.

The slide also severed a nearby highway and appeared to be the latest reminder of geological threats around the rising dam.

Badong is one of the hilly areas along the reservoir that locals recently told Reuters has seen more landslides and tremors since the water level reached 156 metres (512 feet) above sea level last year, increasing pressure on brittle slopes.

Construction of the dam began in 1994 following years of controversy over the plan, which environmental critics call a dangerous folly.

In September, dam officials warned of "environmental catastophe" unless erosion, pollution and geological instability around the reservoir were controlled -- an abrupt departure from bright propaganda about the world's biggest dam.

Since then they have repeatedly said those threats are being dealt with and the dam environment is better than expected.

But now the Three Gorges Project Committee has announced more measures to protect the dam environment, Xinhua reported late on Tuesday.

They vowed tougher controls on towns, villages and factories dumping pollution, and "emergency response" policies to tackle pollution outbreaks.

If all goes to plan, the dam will reach its maximum capacity of 39.3 billion cubic metres of water by the end of 2008. (Reporting by Chris Buckley; Editing by Anne Marie Roantree)

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