In an effort to raise money for African famine relief, Ffyona Campbell, 18, set out yesterday on a walk around the world. The London woman, who abandoned her budding career as a commodities broker, began her trek from a park outside the United Nations. Campbell plans to walk the 3,000 miles from New York to Los Angeles by Jan. 15. From there she will venture to other continents, hiking 20,000 miles over three years.

Campbell said she would be the first woman to complete a round-the-world walk, but that she is more interested in raising money than setting records. She will spend her afternoons talking to the press along her route about hunger and the need for long-term development for Africa.

Two years ago Campbell walked 1,000 miles across Britain in 50 days and raised $35,000 for a London cancer hospital. She has no specific fund-raising goal this time. UNICEF, Live Aid and Band Aid Trust have sanctioned her walk. All the money she raises will be turned over to the Band Aid Trust.

"It will take a very long walk," she said. "But I believe one person can make a difference" . . .