IF YOU'RE an egg-head economist who studies such esoteric subjects as location theory and regional science, it helps to have two major characteristics:

A) An ability to predict the future.

B) A sense of frisky fun.

Walter Isard, an internationally known expert on regional economics as well as the science of establishing a peaceful world in the Quaker spirit to which he adhered, had both.

When in the '50s many economists were predicting that the American steel industry would have its major expansion in New England, Isard said forget it. It's going to happen in Bucks County.

And it did, when U.S. Steel opened its Fairless plant and eventually employed 7,000 people.

Isard further predicted that every job at the steel plant would create five additional jobs - because of the stimulation of retail trade and the attraction of service companies and other businesses.

Then, in the days when people were still getting around in steam trains, he foresaw that airline transportation would become the dominant form of travel.

As a fun-loving father and grandfather, he intrigued his progeny by making up extravagant games and puzzles, including treks to find mythical buried treasure.

And he and his wife were such skilled ballroom dancers, he delighted in teaching his children and grandchildren the old-fashioned waltz.

He also enjoyed playing jazz on the piano and even performed with the legendary Preservation Hall Jazz Band.

Walter Isard, who established the first department of regional science at the University of Pennsylvania, a developer of "peace science," and author of 25 books and 300 papers on his specialties, died Nov. 6 of heart failure. He was 91 and lived in Drexel Hill.

Location theory is the study of how geographic location becomes the prime factor in economic development.

Regional science is the study of the factors that cause a particular industry to locate in a particular place, or how internal migration influences regional economic activity.

He founded the Regional Science Association International and the Journal of Regional Science.

Born in Philadelphia to Jewish immigrants, Isard graduated from Simon Gratz High School and earned a bachelor's degree in mathematics at Temple. He received his doctorate in economics from Harvard and also studied at the University of Chicago, where he met his future wife, Caroline Berliner. They were married in 1942.

Although born Jewish, Isard became a Quaker and signed up as a conscientious objector during World War II. In lieu of military service, he became an orderly in a mental hospital in New York.

In developing the theories of regional science, Isard became the center of a network of scholars from economics, city planning, political science, sociology and geography - all disciplines that affect regional science.

As the world became an increasingly dangerous place, Isard developed the study of peace as a scientific discipline. He wrote many articles and books on arms control and conflict resolution. He conducted seminars on peace science at Cornell.

In 1963, he convened a group of scientists in Malmo, Sweden, to form the Peace Research Society, which became the Peace Science Society International in 1973.

Besides his wife, Isard is survived by three sons, Michael, Scott and Arthur; two daughters, Toni Yagoda and Anni Isard; a sister, Mae Haber; 12 grandchildren and four great-grandchildren. He was predeceased by two daughters, Roberta and Susan.

The family plans a private funeral service.

Donations may be made to the American Friends Service Committee, 1501 Cherry St., Philadelphia 19103-1403.