In the decades ahead, the climb of the world's waters will almost certainly speed up, according to leading scientists. Because of the impending global warming due to the greenhouse effect, more of the water locked in glaciers and, eventually, in the great ice masses of Antarctica and Greenland will melt. Almost as important, the oceans will also expand simply because they are warmer.

The greenhouse effect results from the increase in carbon dioxide and other gases in the atmosphere as a result of industrial activity. The gases allow sunlight to reach earth but absorb energy radiating outward, causing the atmosphere to warm. Scientists are nearly unanimous in predicting a global warming, but are uncertain about its pace. Five-Foot Rise in Century

A decade ago the specter of disaster was evoked by scientists who feared that warming oceans would cause the massive ice sheet of western Antarctica to disintegrate, quickly boosting the seas by 15 feet and flooding major cities. Today most experts believe this is unlikely within the next century or two, and predict that changes in weather patterns will be the most troublesome result of the global warming. Even the revised estimates of oceanic rise, however, spell serious problems for many countries, they maintain.

According to recent calculations by the Environmental Protection Agency, the sea level around much of the United States will climb by one foot over the next 30 to 40 years and by three to five feet over the next century, according to James G. Titus, who directs the agency's research on the problem. These estimates include the effects of the gradual subsidence of land, which is about eight inches per century along the eastern coast.

Other estimates are somewhat lower but still worrisome. A 1983 report by the National Academy of Sciences, for example, predicted a global rise in sea level of about two and one-third feet by 2080, not including the effects of land movements.

When the coastal plain is gentle, as along most of the Atlantic and Gulf coasts of the United States, a given rise in the water level can push in the shoreline hundreds, even thousands of times that distance. The adjustments tend to come in erratic spurts, especially during large storms when a barrier island may roll landward, or a bank of sand dunes may wash away, never to rebuild itself. Hazards Apparent on Long Island

The hazards of shoreline development are already apparent in eastern Long Island, where the beaches are retreating an average of one foot a year. ''There's no question that the sea is rising on Long Island,'' said Larry R. McCormick of Southhampton College. ''As it continues to rise, beaches will grow narrower and narrower and decline in number. The response will be construction of more and more hardening structures to protect homes.''