As midnight approaches in Seoul these days the most peculiar thing that happens is that nothing much happens at all.

City-dwellers no longer scramble madly to catch taxis or buses home or seek out all-night tearooms or discos to stay put until dawn. The more leisurely late-night rhythm of this metropolis of 8.6 million follows a decision by South Korean authorities earlier this month to lift the country's midnight-to-4 a.m. curfew of 36 years.

In Mugyo-Dong, a warren of tiny bars, eateries and nightclubs amid the high-rise office buildings and hotels in downtown Seoul, business now goes on, if somewhat self-consciously, into the wee hours.

Under a pumpkin-colored new moon, revelers pad the alleyways after midnight in the near-zero cold or huddle into streetside stalls where the garlicky aroma of Korean-style barbecue mingles with exhaust fumes from the thoroughfares.

The new nocturnal freedoms are part of a bid by President Chun Doo Hwan to enhance his popularity by showing a readiness gradually to ease government-imposed controls that have become facts of life here.

It is also designed, in theory at least, to help counteract recession by doing away with previous restrictions on the nighttime operations of factories, nightspots, trucking outfits and other industrial facilities important to business activity here.

More important, knowledgeable observers here say, the dramatic gesture was aimed at impressing foreigners--particularly such advanced industrial trading partners and allies as the United States--with the government's efforts to restore political stability since president Park Chung Hee was assassinated in October 1979.

Last October, Seoul was picked as the site for the 1988 Summer Olympics, an event widely considered here as key to boosting the image of both the leadership and the country.

"Lifting the curfew was intended primarily for foreign consumption," said a diplomatic analyst here. "Can you imagine a country that has a curfew sponsoring the Olympics?"

The curfew was first clamped on by the American occupation troops in 1945, shortly after Japan's defeat in World War II and the end of 36 years of Japanese colonial rule.

It remained in place throughout the Korean War and three decades of intermittent political upheaval and hard-won economic growth until Chun ordered restrictions ended at the stroke of midnight, Jan. 4.

His decree does not apply to the 150-mile demilitarized zone along the 38th parallel that splits Korea north and south and bristles with heavily armed troops. The curfew also remains in effect in coastal areas where South Korea worries about infiltration by Communist agents from the North.

In Seoul, 35 miles south of the DMZ, the decision appears to be popular if somewhat perplexing.

"Everyone looked forward to it," said a prominent Korean executive, "but people have been so conditioned by 36 years of curfew that they feel somehow insecure without it. Patterns of behavior will change, but only slowly."

Three-fifths of South Korea's population of 38 million was born during the years of curfew. While the vast majority is now free to roam the midnight streets, Park Seok Hyun, secretary to the mayor of Seoul, said that generally "more people are going home earlier because during curfew they sometimes had to stay out all night. Now there is no deadline, but everyone still has to get up and go to work the next morning."

City officials had worried, Park explained, that "some disorder would occur because of the sudden change. But the crime rate has actually been reduced . . . . More people are out walking the streets."

The number of late-night traffic accidents has also dropped, according to the latest statistics, because cabdrivers under curfew had to barrel through city streets to make sure they got both their patrons and themselves home by midnight.

According to South Korean press reports, the lifting of curfew could create as many as 500,000 to 600,000 jobs nationwide as the entertainment, transportation and manufacturing industries are permitted to operate more freely.

It is still too early to predict whether the economic boom officials here have linked to the relaxation will materialize. But economic analysts remain skeptical.

"Bar owners, hostesses and taxi drivers all thought it would be a chance to make more money," one said. "But, in fact, cabbies have actually lost money because it's no longer necessary for people to make the rush home and pay three to five times the going rate when buses and subways are now operating longer hours."

At the same time, new opportunities for raking in profits have helped the Korean flair for entrepreneurship. Lee Ki Choon, a shopkeeper, said, "There is certainly less tension now. I believe one can work longer and harder and make more money if he wishes."

Han Mi Ja, proprietor of a neighborhood bar, said, "I can't expect a sudden increase of late drinkers, but I'm going to extend business hours till 1 a.m. and see what happens."

The curfew relaxation may have side effects on the tradition of male supremacy here. Asked what she thought of the recent policy change, Kim Mi Ja, a Seoul housewife, said, "I'm glad my husband won't have the excuse any more to stay out all night to avoid a curfew violation."

In addition to the curfew rollback, South Korean authorities this month relaxed restrictions on hairstyles and school uniforms. Military styles were in vogue under the country's spartan dress codes for primary and secondary school students.

"These small changes may not add up to much right now," said one social critic, "but if you look at them optimistically, they might, in the long run, help open up a new mood, a new diversity of thought among the younger generation that has been lacking in the past."