TOKYO — Americans invented the Internet, but the Japanese are running away with it.

Broadband service here is eight to 30 times as fast as in the United States — and considerably cheaper. Japan has the world's fastest Internet connections, delivering more data at a lower cost than anywhere else, recent studies show.

Accelerating broadband speed in this country — as well as in South Korea and much of Europe — is pushing open doors to Internet innovation that are likely to remain closed for years to come in much of the United States.

The speed advantage allows the Japanese to watch broadcast-quality, full-screen television over the Internet, an experience that mocks the grainy, wallet-size images Americans endure.

Ultra-high-speed applications are being rolled out for low-cost, high-definition teleconferencing, for telemedicine — which allows urban doctors to diagnose diseases from a distance — and for advanced telecommuting to help Japan meet its goal of doubling the number of people who work from home by 2010.

"For now and for at least the short term, these applications will be cheaper and probably better in Japan," said Robert Pepper, senior managing director of global technology policy at Cisco Systems, the networking giant.

Japan has surged ahead of the United States on the wings of better wire and more aggressive government regulation, industry analysts say.

The copper wire used to hook up Japanese homes is newer and runs in shorter loops to telephone exchanges than in the U.S. This is partly a matter of geography and demographics: Japan is relatively small, highly urbanized and densely populated. But better wire is also a legacy of American bombs, which razed much of urban Japan during World War II and led to a wholesale rewiring of the country.

In 2000, the Japanese government seized its advantage in wire. In sharp contrast to the Bush administration over the same period, regulators here compelled big phone companies to open up wires to upstart Internet providers.

In short order, broadband exploded. At first, it used the same DSL technology that exists in the United States. But because of the better, shorter wire in Japan, DSL service here is much faster. It's 10 to 20 times as fast, according to Pepper, one of the world's leading experts on broadband infrastructure.

Indeed, DSL in Japan is often five to 10 times as fast as what is widely offered by U.S. cable providers, generally viewed as the fastest American carriers. (Cable has not been much of a player in Japan.)

Perhaps more important, competition in Japan gave a kick in the pants to Nippon Telegraph and Telephone Corp. — or NTT — once a government-controlled enterprise and still Japan's largest phone company. With the help of government subsidies and tax breaks, NTT launched a nationwide build-out of fiber-optic lines to homes, making the lower-capacity copper wires obsolete.

"Obviously, without the competition, we would not have done all this at this pace," said Hideki Ohmichi, NTT's senior manager for public relations.

His company now offers speeds on fiber of up to 100 megabits per second — 17 times as fast as the top speed generally available from U.S. cable. About 8.8 million Japanese homes have fiber lines — roughly nine times the number in the U.S.

The burgeoning optical fiber system is hurtling Japan into an Internet future that experts say Americans are unlikely to experience for at least several years.

Shoji Matsuya, director of diagnostic pathology at Kanto Medical Center in Tokyo, has tested an NTT telepathology system scheduled for nationwide use next spring.

It allows pathologists — using high-definition video and remote-controlled microscopes — to examine tissue samples from patients living in areas without access to major hospitals. Those patients need only find a clinic with the right microscope and an NTT fiber connection.

"Before, we did not have the richness of image detail," Matsuya said, noting that Japan has a severe shortage of pathologists. "With this equipment, I think it is possible to make a definitive remote diagnosis of cancer."

Japan's leap forward, as the United States has lost ground among major industrialized countries in providing high-speed broadband connections, has frustrated many American high-tech innovators.

"The experience of the last seven years shows that sometimes you need a strong federal regulatory framework to ensure that competition happens in a way that is constructive," said Vinton G. Cerf, a vice president at Google.

Japan's lead in speed is worrisome because it will shift Internet innovation away from the United States, warns Cerf, who is widely credited with helping to invent some of the Internet's basic architecture. "Once you have very high speeds, I guarantee that people will figure out things to do with it that they haven't done before," he said.