PUSAN, South Korea, April 1 - Speeding through patchwork landscapes of rice paddies and 20-story apartment buildings, a fleet of blue and gray bullet trains made South Korea decidedly smaller on Thursday.

With sleek new French-designed trains hitting 185 miles an hour, 100 miles an hour faster than older trains here, the new service is already reworking the face of this nation, prompting airlines to cut scores of domestic flights and sending real estate prices soaring in backwaters suddenly seen as future suburbs of Seoul, a capital with Tokyo-level apartment prices.

On the world stage, the bullet trains herald South Korea's coming of age. The next generation of high-speed locomotives under development here is called G7, a clear nod to Korea's ambition to join the Group of Seven industrialized nations.

"Following Japan, France, Germany and Spain, we have become the fifth country to run a high-speed train," the acting president, Goh Kun, said on Tuesday at an inauguration ceremony for the service at Seoul Station. This newly rebuilt terminal of soaring steel and sunlit glass is part of a five-year, $1 billion program to build 12 bullet train stations. When the network is complete, in 2010, the 18-year project is expected to have cost about $17 billion, the largest civil engineering undertaking in Korean history.

High-speed rail, for 40 years a Japanese preserve, is spreading in middle-class Asia as a glut of vehicles slows traffic. In October, Taiwan is to inaugurate a Japanese-built, 210-mile bullet train between Taipei and the southern port of Kaohsiung. By year's end, China is expected to choose a foreign partner to help build an 807-mile high-speed link between Beijing and Shanghai, which could cost $12 billion by 2008. One bidder is Alstom, the French company that provided most of the technology for South Korea's new train.

The new era for South Korea began on Thursday with the start of high-speed service on the first three-quarters of the 253-mile distance from Seoul to here.

In 1970, South Korea showed its industrial ambitions with its first limited-access highway, along the same corridor. But in South Korea, where 48 million people live in an area the size of Indiana, traffic jams now cost the economy about $20 billion a year, largely in lost working hours. While South Korea is renowned for having nearly universal high-speed Internet access, highway speeds can be torturous.

"You can't tell how long it will take to drive - four to six hours minimum," Lee Sook Jeong, a 24-year-old student who hopes to teach English, said of the drive from Seoul to Pusan, her hometown. Relaxing on Thursday in an airplane-style seat on the ride of 2 hours and 40 minutes, she said, "This fast train is cheaper and it's better than planes."

South Korea's goal is to become a business and logistics hub for northeastern Asia. A crucial part of this vision is the high-speed train, officially called Korea Train Express, or KTX. South Korea, the world's fourth-largest oil importer, has high gasoline prices, because all its oil is imported. For the 180-mile drive to Seoul from Taegu, the nation's third-largest city, gas and tolls run $40, while the train is just $35.

High-speed trains could triple passenger traffic on the nation's main line, between here and Seoul, to half a million passengers daily, according to one study. And with the old tracks freed of passenger trains, rail freight to and from this port could increase sevenfold, to three million containers a year.

Korail, the state railroad operator, charges about 25 percent less for tickets than airlines do. The one-hour air hop from Seoul to Pusan may be faster - KTX trains promise to do it in less than two hours - but air travelers have to factor check-in time and travel time to airports.

In a rare victory in modern times for trains over planes, airlines cut 70 percent of flights from Seoul to Taegu and 21 percent of flights between Seoul and here.

To compete, Korean Air said it would cut check-in times in half and would serve hot muffins to early-morning fliers. But the future looks bleak for domestic air travel.

In contrast, Japan's Nozomi super-express trains between Tokyo and Osaka are locked in a price war with airlines. Last fall, after the Central Japan Railway Company invested $900 million in a new Shinkansen terminal for southwestern Tokyo, Japan Airlines representatives walked through the station, distributing leaflets that read, "Dear Nozomi, I'll arrive at the destination first."

Japanese airlines have taken some market share away from bullet trains in recent years. But South Korea's domestic airports are resigned to reinventing themselves as international conduits. Last week, Kimhae Airport in Pusan announced an ambitious plan to seek as many as 72 new international flights, largely to the United States and Europe.

High-speed rail is expected to accelerate another lifestyle change in this country, long notorious for a "develop at any price'' work ethic. Starting in July, South Korean companies are to shift to a five-day workweek, from five and a half.

This city, known for its beaches and islands, is forecasting a 30 percent jump in foreign tourist arrivals this year, to two million. To cater to day-trippers, sightseeing companies are shifting tours to start at the refurbished railroad station. Mokpo, another seaport that is the terminus of the other high-speed branch, is forecasting a 60 percent jump in tourists.

"When the five-day workweek is phased in, people will have more time for leisure, for long weekends," Guy Godet, general manager of the beachfront Pusan Marriott Hotel, predicted here on Thursday. Foreseeing that South Koreans will develop a taste for weekends, Korail is scheduling 122 bullet trains between here and Seoul on weekends, and 104 on weekdays.

In another shift, the high-speed trains are pushing the range of Seoul's suburbs. In Taejon, real estate prices doubled last year in anticipation of commuting times that have been cut to 49 minutes from an hour and a half.

"The high-speed railway will ease overpopulation in the metropolitan areas across the country by encouraging businesses to move to now-provincial areas," The Korea Times said in an editorial on Thursday. "It is certain to emerge as the key means of long-distance transportation, easing chronic traffic on the two main expressways and greatly cutting transport costs for business."

As real estate prices rise, urban planners predict that new service by the fleet of 46 high-speed trains will stretch Seoul into an oval-shaped megalopolis. In Japan, bullet train service has bolstered Tokyo and provincial cities where trains stopped. Greater Tokyo has a third of Japan's population, while greater Seoul has almost half of South Korea's.

The population pressure on Seoul may be eased by cheaper real estate in commuting range and by the government promise to move the capital to a more centrally situated city along the bullet train route.

On Thursday, despite all the balloons and celebrations, some passengers still complained. In Car 12 of the 10 a.m. nonstop from Seoul, several seat rows were facing backward, the drop-down television monitor did not show the train's progress, and there was no hot coffee.

"The seats are quite small, and for me, with a belly, it's a little uncomfortable," said Cho Sang Yoon, an amply built 38-year-old software engineer from Seoul.