In announcing the program, Google offered a glimpse of the benefits of ultra-high-speed Internet service. “Imagine sitting in a rural health clinic, streaming three-dimensional medical imaging over the Web and discussing a unique condition with a specialist in New York,” its statement said. “Or downloading a high-definition, full-length feature film in less than five minutes. Or collaborating with classmates around the world, while watching live 3-D video of a university lecture.”

Such visions of new high-speed services in health care, entertainment, education and business are behind the ambitious national programs under way in countries like Australia and South Korea. Already a leader in high-speed broadband, Korea plans to offer one-gigabit-per-second service nationally by 2012.

Higher-speed Internet service, experts agree, is an important national goal, but it is less clear whether moving quickly to very-high-speed service is worth the cost. Much of the economic gain can be achieved, and consumer demand met, by moving on a more measured path, they say.

Verizon, for example, has invested billions of dollars to upgrade much of its network for fiber optic Internet service, at speeds of 15, 25 and 50 megabits per second. Those speeds are three to 10 times faster than standard broadband service; the monthly charges are $50 for 15 megabits, $65 for 25 and $140 for 50. And the vast majority of Verizon’s fiber optic Internet customers, analysts say, choose the 15-megabit, $50-a-month service.

The demand for one-gigabit-per-second service could be minuscule, experts say. “I can’t imagine a for-profit company doing what they are doing in Chattanooga, because it’s so far ahead of where the market is,” said Robert D. Atkinson, president of the Information Technology and Innovation Foundation, a nonpartisan research group.

Even Mr. DePriest of EPB does not expect brisk demand for the one-gigabit service anytime soon. So why offer it? “The simple answer is because we can,” he said.

And, Mr. DePriest said, it can be done at minimal additional expense, once fiber optic cable is strung to homes and businesses, and the electronics for ultra-high-speed Internet — more than 100 megabits per second — are in place.