Dr. Hekstra's country has been doing that for many decades, and the experience of the Netherlands may prove instructional for much of the rest of the world. For the Dutch, adapting to a sea-level rise means simply an expansion of the elaborate, modern coastal defense system it has developed in the last 30 years. Government studies have shown that to protect the country from a sea-level rise of 1 meter will require an investment, over the long term, of up to $10 billion. The Netherlands has already spent $15 billion on coastal defense in the last three decades.

Coastal defense means building dikes and piling up sand on the coast to strengthen dunes and sculpting rivers and canals to keep sea water from penetrating the soil and ruining both fresh water supplies and agricultural land. Dr. Hekstra said it is his opinion as a private ecologist that all this is well within existing technology and requires only money.

''So I don't think your country and my country is the real problem,'' he said. That is not to minimize the problem, he said, since the United States would have to spend billions of dollars to defend coastal cities and developments against a one-meter rise in sea level and might well have to abandon some low-lying regions altogether.

''We can cope,'' Dr. Hekstra said. ''But not Indonesia, not Bangladesh, not Vietnam. They don't have the resources to do it. Who's going to pay the bill for the developing countries?'' In the United States, the E.P.A. has made extensive studies of the effect of a rise in the sea level, and most coastal states are beginning to plan for it. Questions being examined include not only coastal defense but matters like beach erosion and the intrusion of salt water into rivers and bays where it would foul drinking-water supplies. Possible solutions to salt-water intrusion include the construction of barrier dams in estuaries and canals to divert the salt water from drinking water intakes. Close attention is also being paid to the control of hazardous-waste disposal sites in areas likely to flood.

Most of the efforts are in early stages. But ''I haven't talked to a single coastal state that isn't doing some hard thinking about this and where the government is starting to put together some plans,'' said Thomas W. Curtis, the director of the natural resources group of the National Governors' Association.

South Carolina, North Carolina, Maine and Florida, with sea-level rise in mind, have all enacted standards designed to control construction on their shorelines. Water Resources Shortages Likely For California

Some predictions of climate change, admittedly chancy, forecast drier conditions for much of the American West, with serious consequences for a region where water scarcity is already a major factor of life and prosperity. The E.P.A. study for Congress, for instance, found that California's water demand could increase, even as water supplies decrease. The decrease would come about partly because more snow would melt in the winter and less in the summer. Since reservoirs do not have the capacity to store all the winter runoff, spring and summer water supplies would drop.