National Food and Agriculture Stabilization Act - Provides that loans and purchase levels established pursuant to the Agricultural Act of 1949 shall always be available at a minimum of two-thirds of the established prices for wheat and feed grains. Provides a new formula for payments to producers of wheat, feed grains, and upland cotton in order to encourage production of such crops through crop year 1978. Provides, with respect to the 1975 through 1978 crops of wheat, grain sorghum, cotton, oats, and barley, that the Commodity Credit Corporation shall not sell any of its stocks of such commodities at less than 150 percent of the established price applicable by law to the current crop of any such commodity. Prevents the recall of price-support loans on wheat, feed grains, cotton, or soybeans prior to the expiration of three years from the date on which such loans were made in the case where such commodities are held privately for sale. Establishes 90 percent of the price of the commodity as the rate for loans to producers of wheat, feed grain, or upland cotton whenever the Secretary estimates that the carryover stocks of such commodities will fall below specified levels. Requires an export license for carryover stocks the supply of which is determined to be critically low. Establishes the support price of milk at not less than 90 percent of the parity price therefor, and states that this level shall be effective through March 31, 1978.