WASHINGTON (AP) _ This year's World Food Day observance by the Agriculture Department is shaping up as a tribute to the small farmer, with a dash of show biz to brighten the festivities.

Actually, the Food and Agriculture Organization of the United Nations adopted ''The Small Farmer'' as this year's theme for World Food Day, an annual observance since 1980. It is scheduled to coincide with the anniversary of FAO's founding on Oct. 16, 1945.

The USDA is expanding the theme of Friday's observance to highlight the contributions of historically black colleges and universities. Stage and television actress Esther Rolle and soprano Annette Pierson Poulard will join educators and government officials on the program.

A formal proclamation issued Wednesday by President Reagan was put into the works by Sen. Patrick Leahy, D-Vt., chairman of the Senate Agriculture Committee, and 58 co-sponsors in support of the annual World Food Day tribute.

The program Friday will include comments by Agriculture Secretary Richard E. Lyng, who will talk about 21st Century small farmers; and Frederick Humphries, president of Florida A&M University, who will discuss the future role of agricultural universities as partners of small farmers.

Jay Levy, an FAO spokesman, said more than 140 countries are participating in this year's World Food Day activities.

Much has changed since the United Nations convened a world food conference in Rome in 1974. At that time, it appeared to many observers that population growth would outrrun food production, raising the specter of widespread famine.

But global food production, particularly in the developing nations, was able to keep pace, although some individual countries continue to suffer chronic food shortages, drought and famine.

The FAO now says that 1986 world food production was a record, easily outstripping population growth. Food reserves currently are estimated at 24 percent of a year's consumption, well above what the FAO considers to be the global safety margin.

But the number of undernourished people also has increased, according to FAO analysts. Their problem is a lack of money, not a lack of food on the world market.

A recent FAO report said that ''in all developing nations, the poorest people go without, not because of food scarcity but because they lack the money to buy it.''

In the United States and in many other countries, the main agricultural problem has been surplus production, particularly of grain crops.

The magnitude of world food production can be hard to grasp. Reports by the USDA deal in billions of pounds and millions of tons.

Meat production in the major countries, for example, is expected to total 137.2 million metric tons next year, up 2 percent from 1987. Each metric ton is equal to about 2,205 pounds. Virtually all will be consumed.

Grains are different. They can be stored for years until consumed by humans or livestock.

Wheat production is forecast at 507.4 million tons, more than 18.6 billion bushels. According to USDA estimates, 520.1 million tons will be consumed in 1987-88.

But there is plenty of wheat in storage bins to help make up the shortfall. Department experts say that even after deducting the 1987-88 consumption, more than 134 million tons of wheat will still be in storage. At that point another harvest will be ready.

---

WASHINGTON (AP) - Agriculture Department officials say the South's entire cotton belt stands to benefit from techniques used in North Carolina to eradicate the boll weevil.

The department's Agricultural Research Service reported Wednesday that North Carolina's cotton acreage increased 150 percent since the boll weevil was eradicated in 1980 and that the cotton industry has invested $12 million in new cotton gins and gin improvements.

''Eight new gins have come into the state since then and we expect more as cotton production increases,'' said Willard A. Dickerson Jr., an entomologist with the USDA agency in Raleigh, N.C. ''Gins separate cotton fiber from seed and are a key indicator of the industry's health.''

Cotton production in North Carolina rose from about 40,000 acres before the weevil was eradicated to more than 100,000 acres today, Dickerson said.

Growers are averaging about $77 per acre more because of weevil eradication, according to a recent economic study, the agency said. That includes pesticide savings, increased yields and switches to cotton from less profitable crops.

The weevil was wiped out in both North and South Carolina by a program that began in North Carolina in 1978, involving USDA technicians and scientists, local growers and agencies. Growers paid 70 percent of the cost and the USDA paid 30 percent.

Officials said the weevil has been eradicated from 220,000 acres in the Carolinas. This fall the program began on about 375,000 acres in Georgia, Alabama and north Florida.

The program includes malathion spraying to kill the weevils, followed by specially designed traps to catch strays and monitor weevil movements.

Officials said the goal is to establish a weevil-free cotton belt from North Carolina to Texas. The cotton boll weevil entered the United States from Mexico in the 1890s and was established across the South by the 1920s.