The United Nations Food and Agriculture Organization, over the objection of the United States and other industrial nations, moved this week to establish a new worldwide system of seed banks and a fund to support it.

The new system calls for spending $100 million a year to stockpile seeds, cuttings and other germinal material, and to give Third World countries the training and technology to cross-breed seeds to produce heartier plants.

Ultimately, the world's food supply is dependent on the cross-breeding of seeds, cuttings and roots. These billions of plants and seeds, gathered in storage, are called germplasm. Today, germplasm generally is controlled by industrialized nations, but is freely used by underdeveloped and developed nations.

Disputes between the Third World and industrialized nations stem from a supply-and-demand problem: almost all world food crops come from seeds found in the Third World that then are made into supercrops in the developed nations through breeding and cross-breeding with varieties drawn from seed banks.

Virtually all food crops on the market undergo many cross-breedings to impart resistance to disease and to increase yield. This requires seed banks, where many varieties of plants with different traits are stored.

A more immediate point of contention is a clash between free enterprise and state control. The proposed new system would not allow patenting of new seed forms, as can be done at present. This is of particular concern to the United States.

The new U.N. system would be similar to the established germplasm banking system, but would differ on a few sensitive points:

*Control would shift from the industrial nations to the Food and Agriculture Organization (FAO). Third World nations have a voting majority at the FAO.

*More money would be put into the program to give Third World nations the technology and training to perform sophisticated cross-breeding of plants.

*Patenting of seeds would not be recognized. Any seeds or other germplasm collected for the bank could, in theory, be drawn out by any nation. Under U.S. law, companies can patent seeds if they make plants with substantially new sets of traits, such as wheat that has both high yields and resistance to several diseases or pests.

Without cooperation from the major industrial nations, the proposed system is unlikely to work, because it would require substantial funds and technical help.

The fight within the FAO started several years ago with charges from Third World nations that the industrial nations were guilty of "genetic imperialism" because they took seeds at will from Third World nations to use as they pleased.

The FAO now has agreed to begin planning an international network of germplasm banks and research labs. The group also told the FAO director general to study the establishment of a world fund to support the network. The study would be the first step in the attempt to set up a fund at the FAO's next meeting two years from now.

The U.S. position is, as two State Department officials said, "If it ain't broke, don't fix it."

Several germplasm centers now operate with the help of the FAO, but are under the control of a Consultative Group on International Agricultural Research. Under CGIAR is a technical board that works with seed collection, storage, and research labs around the world.

The new initiative would attempt to bring the technical board under FAO control. The FAO would then set the rules about how germplasm is to be collected, and to whom dispensed. The new system, proponents say, would remain open, allowing any nation to draw seeds from the banks.

But U.S. officials say they will not allow the present system to be brought under FAO control. This poses the possibility of duplicate systems.