A dirty problem meanders from East to West. Elbe River: how possible for foes to cooperate in costly cleanup?

Mud dredged from the bottom of this West German harbor is so loaded with pollutants, it's considered a hazardous waste. But the source of the problem lies hundreds of miles away - up the Elbe River in the heart of East Germany and Czechoslovakia. It's there, say West German officials, that factories and towns dump most of the wastes which get carried down-river into Hamburg.

The Elbe highlights how tough it can be to get East and West to cooperate on cleaning the environment.

``Unfortunately, almost all the streams in Europe flow east to west,'' says one West German official.

In the case of the Elbe, this means massive problems for West Germany. The Elbe is one of Europe's dirtiest rivers - with a drainage basin that includes the most heavily industrialized corner of Czechoslovakia and most of East Germany. Every year, more than 20 tons of mercury are washed down the river, about seven times the amount carried by the much larger Rhine.

When the Elbe broadens into Hamburg's network of waterways, it slows - depositing sediments laced with mercury, other heavy metals, toxic chemicals, and organic wastes.

That's where Hamburg's troubles begin. The city dredges about 1 million tons of mud annually to keep shipping channels open. The material once was used to fill marshland or fertilize fields, but this is no longer safe. The dredge piles themselves are now a hazard - since pollutants from the mud can leach into groundwater.

Officials are scrambling to find some way of disposing of the stuff, but admit they're facing a crisis. In an ironic twist, the West Germans are negotiating shipping the material to East Germany for disposal. The East Germans would get hard currency from the deal. ``We always have to keep the option open to ship the material abroad,'' says Harald Go"hren, assistant director of Hamburg's harbor authority, which oversees dredging operations. ``But we hope we don't have to do that.''

And the problem doesn't stop in Hamburg. Only about one-third of the river's wastes get snared in the harbor; the rest are washed through to the North Sea. That body of water is the focus of growing international concern because of the damaging effects pollution already has had on wildlife in the area.

And so the pressure is on to attack the problem at its source.

All three countries involved say they want to clean up the Elbe. But a mesh of economic and diplomatic problems has made progress difficult.

``This isn't just a two-sided problem. It is a problem that has to be dealt with among all three parties,'' says a spokesman for the Czechoslovakian Embassy in Bonn.

Indeed, he says his government is eager to take action. Last October, Czechoslovakia and West Germany signed an agreement which laid the foundation for environmental cooperation on a range of issues. It didn't, however, spell out specific measures aimed at the Elbe.

The key sticking point is a border dispute. The East Germans claim their boundary with West Germany runs down the middle of the river; the West says it runs along the East German bank. The squabble makes for strange conflicts, such as the dispute over how to measure the amount of waste that crosses the border into West Germany.

The West Germans have a water- quality monitoring station at Schnackenberg - near the point where the Elbe leaves the East German heartland to form the boundary between the two countries. But the East Germans insist the river doesn't leave their jurisdiction until much further down-stream.

But even if the border dispute could be settled, there's the much larger question of money. East Germany and Czechoslovakia are hesitant to invest in costly water purification equipment, since this means diverting cash from other industrial projects.

In the past, the West Germans have been willing to pick up the tab for some environmental ventures in the East. In 1982, for instance, Bonn agreed to pay the equivalent of $36 million to help build a water treatment plant on the Spree River - which flows from East Germany into West Berlin.

``But we have to think twice before we do this sort of thing on a large scale,'' says an official at Bonn's Ministry for Intra-German Relations. ``It's a question of fairness. It's not acceptable if the [East Germans] say: `We'll cooperate, but only if you pay.'''

A more likely formula, he says, is for the West Germans to provide technology and expertise to the East in a sort of environmental joint-venture.

Indeed, such an offer has already been made concerning another highly polluted river which flows into West Germany from the East - the Werra. But nobody expects sudden progress. The two sides have been negotiating over the Werra for 14 years, without results.

Meanwhile, nobody's sure what it would cost to clean up the Elbe. One estimate puts the cost alone of building sewage treatment plants in Czechoslovakia and East Germany at more than $3 billion.

The exchange of environmental information between East and West is still extremely sensitive. Not only do East-bloc governments consider it embarrassing to reveal what they dump, they also worry that the data can be used to analyze their industrial capacity. Indeed, in East Germany it's illegal to publish water- quality data.

``We get lots of requests from East German scientists asking for studies,'' says Gerd Flu"gge, director of the Hamburg-based Elbe water monitoring project. But if he asks for information in return, he says, the request is always turned down.

Even if a pact to clean up the river were signed soon, it would take years for the Elbe to flush itself clean.

All the more reason to press for action, say officials in Hamburg. The port authority is now rushing to build a special sifting machine that would separate out the most polluted parts of the mud - which could then be heaped into small hills separated from the ground below by plastic liners.

This would solve the problem for about 15 years, says the harbor authority's Dr. Go"hren. But the city is growing impatient, he says. Earlier this summer, officials here threatened to sue the West German government, unless more is done to launch an international cleanup.