Plan for farming earth's oceans; Seafarm, by Elisabeth Mann Borgese. New York: Harry N. Abrams Inc. $35.

Elisabeth Mann Borgese looks at the ocean and sees an unplowed field. As chairman of the International Ocean Institute in Malta and a staunch proponent of aquaculture -- the farming of seas, lakes, rivers, and ponds -- the author envisions a world in which fish and seaweed become mankind's bread and butter, helping to feed an ever-expanding population. Mrs. Borgese, daughter of novelist Thomas Mann, is well known for her efforts in seeking international cooperation in the development of marine resources.

In this worldwide survey, the reader is taken from tide-swept oyster "parks" in Brittany to bamboo-fenced milkfish farms in the Philippines.This overview shows the historical development of aquaculture, along with the most prevalent techniques in use today.

Many color photographs and illustrations give the text a visual dimension -- the reader sees the rough wooden sluice gates that hold back water in an Indonesian hatchery and the face of the man who dives for mussels in the Gulf of Siam. In fact, in some instances, the pictures overshadow the text.

But beyond the picture of aquaculture as it now exists lies of message: Farming the sea must no longer be considered simply a curiosity; it must become a major source of food. Yet the development of aquaculture is still primitive, frozen into patterns established thousands of years ago in many parts of the world.

In one chapter, the author offers a list of reasons for developing aquaculture in a big way. She points out that since the first farmers began tilling the soil, man has been placing greater and greater demands upon the land. Today, more than 96 percent of our food is raised on good old terra firma. But with expanding populations continually subdividing and scarring our once fruited plains, the author points out, "We have to recognize that the possibilities of expanding agriculture are very limited, and that the limits themselves are shrinking."

Borgese, who has been active in the Conference on the International Law of the Sea at the United Nations, builds a convincing case for aquaculture. After all, the idea of feeding the multitudes has a humanitarian appeal which is hard to beat.

However, the book also considers the potential problems -- environmental, political, and social -- that large-scale aquaculture might bring. For instance , in cultivating fish for release into oceans, countries bordering the ocean may dispute fishing rights.Why should one country stock the sea, only to have its neighbors reel in their efforts? There are also environmental concerns raised by tampering with marine environments, such as introducing new species which may damage existing flora and fauna.

But in dealing with the problems of aquaculture, the author reveals a blatant political bias which may repel some readers. The survey is laced with references that suggest that government ownership is superior to private development -- both economically and philosophically.

The author maintains that aquaculture resources should be managed "for the benefit of all countries" through an international organization that would ensure the distribution of food according to need as well as participation. "What is needed is a new law revolutionizing our concepts of ownership and sovereignty and transcending the legal bounds of a dying past," she writes.

This simplistic socialistic approach to the complex problems of large-scale aquaculture weakens and otherwise well-researched, colorful, and readable book.