THOUSANDS of anti-nuclear protesters are planning a demonstration tomorrow to disrupt the first shipment of reprocessed atomic waste to Germany for four years.

They will be met by more than 15,000 riot police and border guards who have been drafted in as an armoured train takes the radioactive waste to a storage depot near the village of Gorleben, in Lower Saxony. Officials fear violence, and dozens of temporary prison cells in portable cabins have been set up for arrested troublemakers.

The demonstration has been organised by Germany's powerful anti-nuclear movement, which says that the federal government of Social Democrats and Greens has not been radical enough in its plans to abolish atomic power over the next 20 years.

The action is a particular embarrassment to the Greens in the coalition, who have hailed the resumption of shipments of German waste from a French reprocessing plant as an important step in the nuclear phase-out plan. Jurgen Trittin, the Green Party Environment Minister, maintains that the return of spent fuel heralds "the beginning of the end of nuclear power" in Germany. "No other industrial country is abandoning nuclear power more quickly," he said last week.

Mr Trittin's appeals, however, have failed to convince protesters, who oppose such shipments. Wolfgang Ehmke, a veteran protester from the Gorleben area, said: "The Greens in government no longer consider themselves part of the anti-nuclear movement. We will not allow ourselves to be gagged."

Demonstrators are expected to descend tomorrow on Gorleben where they will try to block the progress of the train carrying the waste in reinforced steel containers. The region was the scene of previous anti-nuclear protests before the government called a temporary halt to such shipments four years ago. This time, officials are attempting to defuse potential unrest by dispatching 130 police "conflict managers", dressed in bright red anoraks, who will be on hand to negotiate with protesters.

Early signs of trouble came last Wednesday when masked protesters attacked the Berlin offices of German Rail, which will ship the nuclear waste. They shattered 78 windows, threw tear gas grenades and fled on bicycles. It was the ninth attack on railway buildings since plans for the nuclear shipment were announced. The protest movement's website carries detailed instructions on how to use grappling irons to cripple the railway's overhead power cables, damage lines and tunnel under roads to prevent nuclear waste shipments by lorry.

Opposition is not confined to militants. Jochen Flasbarth, the director of Germany's environmental umbrella group, Naturschutzbund, said: "We will continue to exert pressure because the dangers of atomic energy have not been reduced." The Green Party had not bargained for this rank-and-file rebellion which has split the environmental movement and may cost the party votes in the next general election, due in 2004.

The party sees the scrapping of nuclear power as one of its main policy objectives. Despite considerable opposition from within the nuclear industry, Mr Trittin was able to announce last year that he had achieved a consensus with energy providers, establishing a basis for a complete end to atomic power over the next 20 years.

Under the arrangement, the industry agreed to end nuclear reprocessing by 2005. The first part of the deal involves Germany fulfilling its legal obligation to France by taking back nuclear fuel rods sent to a plant at La Hague for reprocessing. The waste remains highly radioactive and must be carefully stored.

In an attempt to placate grassroots opinion, Claudia Roth, the Green Party leader, insisted last week that the anti-nuclear movement had every right to demonstrate peacefully at Gorleben. Waning support for the Greens is not confined to the anti-nuclear lobby. The party's wholesale commitment to abandoning nuclear power is being undermined by warnings from scientists that the resulting, inevitable increase in the use of fossil fuels will speed up global warming.

No law has yet been passed that formally ratifies the abandonment of nuclear power. Wrangling over the final draft continues between Mr Trittin and the Industry Minister, Werner Mueller. Fears remain that any future law could be challenged either by the energy providers or by the anti-nuclear lobby in Germany's constitutional court, which could rule it null and void.

None of the parties involved has been able to answer a vital question posed by the shutdown plan: where to store the atomic waste - which remains radioactive for 24,000 years - that will accrue from the country's 19 nuclear plants when they close. Plans have been drawn up for the provision of so-called final depots for nuclear waste by 2030, but if Gorleben is anything to go by, opposition to such sites is likely to be considerable.