A recent Post article {"Ironing Out the Greenhouse Effect," news story, May 20} discussed the suggestion that the polar seas be fertilized with iron in order to stimulate an enormous bloom of tiny marine plants (phytoplankton). Some scientists believe this would remove enough carbon dioxide from the atmosphere to reduce the rate and extent of global warming. However, the proposal is flawed in a scientific sense and furthermore reflects an imprudent attitude toward nature that has wreaked ecological havoc in the past.

The feasibility of using iron to produce huge phytoplankton blooms depends upon the tentative findings in a few studies that phytoplankton growth is held in check only by iron. However, the evidence that phytoplankton growth is controlled by light and temperature in polar oceans remains more convincing at this time.

Furthermore, it is by no means clear that increased blooms would reduce the amount of carbon dioxide in the atmosphere. Unless the carbon taken up by phytoplankton sinks to the deep ocean, the phytoplankton bloom will have no large effect on atmospheric carbon dioxide, and hence it will not alleviate global warming.

Iron has the potential to alter the kinds of phytoplankton that will grow in the polar ocean, since different species have different abilities to use the iron. Changes in the phytoplankton species may result in changes in the food web that ultimately determines how much carbon sinks to the bottom. Such alterations might not only make the iron addition ineffective, they would also severely disrupt the penguin, whale, seal and fish populations that depend on the existing food web.

Small-scale experiments would be useful in advancing our understanding of how ocean productivity is controlled, but would be virtually useless for addressing the carbon dioxide "clean-up" hypothesis. Current understanding of how the oceans work is not sophisticated enough to allow us to scale up the results of small experiments to global dimensions.

Farfetched technological attempts to "fix" global warming distract us from prudent policies that address the sources of the problem: fossil fuel combustion and deforestation. Energy efficiency can buy us time and save us money. Stopping deforestation will protect biological diversity and enhance soil conservation while at the same time decreasing the risk of global warming. We must ultimately switch to renewable sources of energy if we are to eliminate all of the other clear and present problems of fossil fuel use: oil spills, air pollution and acid rain.

We are incapable of making even minor modifications of terrestrial ecosystems that are relatively well understood without unanticipated and unfortunate consequences. We have no business conducting large experiments on poorly understood marine ecosystems, particularly when there are far more attractive policy options available. RODNEY M. FUJITA Staff Scientist MICHAEL OPPENHEIMER Senior Scientist Environmental Defense Fund New York