When Kurisumasu comes to Tokyo there are no silent nights.

In Roppongi, one of the city's half-dozen chic shopping districts, the familiar strains of yuletide Muzak blare from the McDonald's and Kentucky Fried Chicken outlets.

Brightly lighted evergreens dot the teeming sidewalks as shoppers hustle through the cold, pausing before frosted shop windows silhouetting cutouts of Santa and his sleigh.

Taxi drivers lay on their horns in the bumper-to-bumper traffic as gaggles of boisterous Japanese office workers, arms linked, careen through the narrow back alleys where neon signs advertising the area's hundreds of restaurants and bars run up the sides of buildings.

By mid-December, the high sense of decorum and efficiency with which the Japanese normally go about their business has all but vanished as this prosperous, consumer-oriented country plunges in its annual binge of year-end merrymaking and gift-giving.

That the Japanese have gripped Christmas with a passion since World War II may seem strange to foreigners. In this Asian country with age-old Buddhist roots, less than 1 percent of the 117 million inhabitants are practicing Christians.

This hardly bothers the Japanese, however, who are old hands at borrowing things foreign and absorbing them with a uniquely Japanese flair. Christmas--an unofficial holiday here--reflects a blend of slick commercialism on the part of Japan's enterprising retailers and a centuries-long tradition among the Japanese of plying bosses, clients, influential individuals and friends with seasonal gifts.

In Japan's rigidly hierarchical society, the custom of giving year-end gifts, called oseibo, used to be intended as a gesture of repaying individuals for weighty personal obligations piled up over the year.

Today, this custom has been nudged aside and presents--ranging from fancy gift packages of dried seaweed, Japanese green tea and imported whiskey to considerably more costly items--are often given with an eye toward future advancement.

To a young businessman, a gift given to immediate bosses may be viewed as a way to protect his position in the company pecking order in advance of of annual promotions after New Year's. Parents may feel obliged to make offerings to teachers, especially those at highly competitive private schools.

The overlay of Christmas spirit has helped spruce up the once onerous image that marked the season. "It's in the Japanese pyschology to thank those we think we owe at the end of the year," explained Masahide Sakauchi, an advertising executive at Tokyo's Takashimaya department store. "Oseibo used to have a very gray image--people think of canned hams--but Christmas, with all its colorful decorations, is bright and romantic."

Armed with year-end bonuses equal to about three month's salary, Japanese workers mob major department stores such as Takashimaya, where spending is encouraged by computerized gift-selection centers. The buying spree usually peaks on the Sunday before Christmas. This year, Takashimaya's main Tokyo store hauled in $7 million in sales on Dec. 20, despite a minirecession in the economy here.

Behind the Madison Avenue-style marketing blitz lurks a host of traumas for ambitious company men who must calculate the dangers of offending their bosses by giving too much or not enough.

"It's a real headache," said a junior executive, "because if you give too much it's not considered proper and if you don't give enough it's worse." These offerings may range from a $10 bottle of whiskey to designer lighters or tie pins.

A senior executive at a major company here, who regularly receives gifts from his juniors even though he has openly discouraged the practice, said, "One of my employes used to complain that gift-giving was a stupid custom. Recently, however, he has changed his tune and insists he must do something to show his gratitude. He's now approaching 40, which is a critical age for promotion in the company."

While many Japanese companies have tried with only limited success to put a stop to this tribute system inside the office, the executive pointed out, companies spend exhorbitant sums annually to send presents to major clients, customers and the government bureaucrats with whom they must deal regularly.

Although the Japanese tend to see nothing wrong in greasing the wheels of personal and business relationships with gifts, provided the value of items stays within acceptable bounds, the government moved two years ago to crack down where public servants are involved.

Hiroshi Fujita, who supervises bureaucrats' conduct for the prime minister's office, said: "Officials should not receive any gifts relating to their jobs and, if they do, they should send them back." Presents from foreign officials or politicians worth more than the equivalent of $100 must be returned or handed over to the proper authorities.

The increasing popularity of Christmas here, however, has added a more personal flourish to the season among a younger generation. As in the United States, children have become the center of a now firmly entrenched custom of family gift-giving.

In the toy section of Tokyo's large Matsuzakaya department store, Yume Nemoto, 23, said, "The Christmas custom has become more established year by year." Wearing a tastefully tailored Santa costume for her role as "Sister Santa," the store employe explained, "People are getting more enthusiastic about buying gifts for their kids. Parents come in with their kids and let them choose what they want. Then they tell me to wrap up the things in Christmas paper with a note from Santa."

While Santa may be a relative newcomer to Japan, he appears to have made a hit with Japanese children.

"I don't know where Santa comes from," said Yuzuru Hashimoto, 7, "but I believe in him because I've got a lot of good games from him."