Congressional Budget Office Reports

onAgriculture has this 1989 report "Agricultural Progress in the Third World and its Effect on U.S. Farm Exports " which seems to be a good primer on agricultural trade. I came to it after reading a 1987 NY Times article that there were protests by various farming groups about US agricultural aid to developing countries. These reports are supposed to be 'objective' evaluations of the situation and do not make any policy recommendations. It notes (in 1989, page 3 of the report):
"China and India, on the other hand, are success stories. Not only have they maintained positive growth in income and investment over the last 20 years, they have raised their growth rates during the 1980s, a period when most developing countries have floundered....Much of the success in China and India can be
attributed to reductions in government controls and more reliance on market forces."
In the summary and conclusions part, it explains why aid to developing countries is important for US:
"Like other sectors of the U.S. economy, agriculture depends increasingly on trade with developing countries—that is, the more than 100 countries that have not yet become fully modern and industrialized. Exports of farm products to developing countries have grown fivefold since 1970, representing about 41 percent of all U.S. agricultural exports in 1987. Developing countries buy more than two-thirds of U.S. exports of food grains. Such trade is expected to become even more important in the future.

This report centers on food. Food policy is the primary focus of agricultural policy in most developing countries, and food products are the main agricultural imports of developing countries and the principal agricultural exports of the United States.

Recent research has found that many developing countries tend to increase their imports of food as their agriculture develops. Two key relationships hold here: advances in agricultural efficiency, often accompanied by greater agricultural output, contribute to overall economic growth and higher incomes; in turn, higher incomes stimulate the demand for food. In many cases, the demand for food grows faster than the supply of food, resulting in greater food imports. These linkages help explain the apparent paradox that impressive gains in agricultural production by developing countries overall have been accompanied by solid growth in their agricultural imports—and notably in their imports of U.S. farm products. The evidence argues strongly that the encouragement of economic growth in developing
countries, including (and in many cases especially) agricultural development makes sense not only from the humanitarian and foreign policy standpoints but also in the narrower terms of U.S. economic interests. These generalizations represent a view now widely held by development economists. "
From page 38:
"A vibrant agricultural sector stimulates the whole rural economy, further increasing the demand for rural labor. Many gain, but not all. Those who suffer the most tend to be poor. The factors that lead to stronger agricultural performance-such as technological advances, increased use of machinery, and higher prices for farm output-penalize those workers whose jobs are replaced by machines and who cannot find new, comparable employment, as well as those who cannot afford to pay higher prices for food. In both cases, those at the bottom—the landless and unskilled throughout the country, especially children and women—tend to bear the greatest burden.
Governments in developing countries need to protect the poor from the negative effects of economic growth. This may call for policies to assist the poor, possibly at some cost in economic growth. The only long-run solution for poverty, however, is to create constructive employment for the poor, which is integrally linked to development of the agricultural sector."
On food security (from pages 39-40)
"Food security does not imply self-sufficiency at any cost, but having the resources to meet short-term supply disruptions.
....
International trade is a key element of any nation's food security. In general, depending on their specific resource endowment, agriculture-based economies should supply most of their own staple food needs."
The last chapter notes the decline of US aid, different components of US aid, aid as a lever of foreign policy and various criticisms of US aid. I have read large portions of the report and the whole report seems worth reading and comparing with recent reports.