Barbara Ward, 67, a British journalist and economist who was one of the most eloquent voices calling for aid to the underdeveloped Third World and was an early proponent of world environmental policies, died of cancer yesterday at her home in southern England.

Miss Ward was the author of more than a dozen major works on economic development, written for the layman as well as the professional economist. She served on United Nations and Vatican commissions dealing with the sharing of world resources, and was a friend and adviser to statesmen on five continents.

Although she never held elective office, nor served in a government, she exerted profound influence on the debate surrounding the relation of rich to poor nations.

Honored for her writing, she also was an accomplished speaker, and an English radio personality.She was voted the second most popular public speaker in Great Britain in a 1944 national poll. She had written and had been foreign editor for the Economist, a highly respected British news weekly, and had lectured not only in Britain but at Harvard and Columbia universities.

Miss Ward's major works included "The International Share-Out," published in 1938, "Spaceship Earth," in 1966, and "The Widening Gap," published in 1971, and "The Home of Man," which appeared in 1976. A 1972 book she wrote with Rene Dubos, "Only One Earth," was used as the theme book for the United Nations Stockholm Conference on the Environment that same year.

Reviewing this book, one critic wrtote that Miss Ward described "the dilemma of the poor nations -- called to modernization and industrialization in order to raise their people from misery, yet hindered by the rich nations' traditional exercise of power and now by a new concern for pollution and ecological balance."

Another of her books, "Nationalism and Ideology," was hailed in the (London) Times Literary Supplement as a brilliant summary of man's progress from the tribe to the nation-state.

Her books and speeches to audiences brought home her hopes and her fears for the future, and a feeling that much of the future would be determined by the relationship between the rich and poor nations of the planet.

In "The Rich Nations and the Poor Nations" (of which Lyndon B. Johnson once said "I read it like I do the Bible") she wrote, "If we are to face the vast gap between the nations around the Atlantic area which have been through their modernizing revolutions and the searching nations all around the world who seek desperately to make the same transition, perhaps the first decision we have to make is to abandon the fallacy that, somewhere, somehow, everything is going to turn out all right."

In a 1964 speech in Washington she said that modern science and technology had unlocked "the gates of absolute scarcity" and made it a matter of choice whether to feed and clothe the world's poverty-stricken. "Never again can we say: 'We would have done it if we could, but the means were lacking.'"

In another Washington speech that same year she asserted that the "possibility of making the desert bloom is just as stirring as going to the moon."

At the bottom of all her pleas was the theory that foreign aid, "direct transfers of wealth from rich nations to poor nations," is the solution to many world problems. She appealed to the Free World to invest money to help the underdeveloped nations "come through the sound barrier of modernization."

Among her students and admirers was President Johnson, who borrowed from Miss Ward her phrase, "the ancient enemies of mankind," as a call to use foreign aid to attack world poverty, disease, and ignorance.

Other American public figures she advised included John F. Kennedy during his presidency, World Bank President Robert S. McNamara, and Robert Kennedy, before and during his bid for the 1968 Democratic presidential nonmination.

Miss Ward was appointed to the Pontifical Commission for Justice and Peace in 1967. The commission studies ways of helping poor countries. Miss Ward, a prominent Catholic lay person, recommended that the church donate some of its wealth to developing nations.

She was a past president of the International Institute for Environment and Development and was council chairman of the organization at the time of her death. She also had been a member of the Adlai Stevenson Institute of International Affairs since 1968.

Miss Ward was born in York, England. Her father was a solicitor of Quaker leanings and her mother was a devout Roman Catholic. Miss Ward was reared in her mother's faith.

At the age of 15 she went to Paris where she spent two years studying at the Lycee Moliere and the Soronne, then went to Germany where she attended college in Jugenheim. After spending three years at Somerville College, Oxford, she took a first in modern greats in 1935.

During the next three years she studied abroad in Europe during the summer and lectured at Cambridge University during the school year. She became a staff writer with the Economist in 1939, and served as the magazine's foreign editor from 1940 to 1950. She served on the staff of the BBC from 1943 to 1946, and on its board of governors from 1946 to 1950.

She first came to this country in 1942 and worked for the British Ministry of Information in Washington during World War II.

She was a visiting professor at Harvard University from 1958 to 1968, and was Albert Schweitzer Professor of International Economic Development at Columbia University from 1968 to 1973.

Five years ago, Miss Ward was made a life peer with the title of Baroness Jackson of Lodsworth. Last year she received Britain's Royal Society of the Arts Albert Medal, and India's Jawaharlal Nehru Memorial Award for International Understanding. She donated the money from both prizes to an Indian leper colony.

In 1950 she married Sir Robert Jackson, a United Nations official. He survives, as does a son.