TOKYO - Baby carriages are a rare sight on Tokyo streets. Rural areas are nearly devoid of youngsters. These are just the most obvious signs of a trend that's strangling the country's future, as maternity wards shrink and kindergarten classrooms are abandoned across Japan.

Worried about their futures and unwilling to commit to others, a generation of Japanese is shunning marriage and childbirth, giving their nation one of the world's lowest birthrates, with profound consequences. A steadily shrinking labor force promises to starve the world's second-largest economy just as baby-boomers swell the ranks of retirees. And as Japan's population declines, so will its influence.

Japan's birthrate is 1.3 per woman per lifetime, compared with 2.1 in the United States. The nation's population will begin shrinking in 2005, and in 25 years, more than a third of Japanese will be 65 or older. And unlike other nations confronted with shrinking birthrates, such as Italy and Germany, homogeneous Japan gives no sign that it will welcome foreign immigrants to supplement its depleted workforce.

Like the hundreds of thousands of men who lock themselves in their rooms to escape the pressures of a rigid social system, Japanese women fear being trapped in marriage and are disengaging from traditional family roles. Smarter and better educated than any previous generation, they're unable to find companies that accept working mothers or husbands who embrace working wives.

Marriage age rising

Until the late 1960s, the average Japanese woman first married when she was 24 1/2 years old. A woman who didn't marry by 25 was considered ``Christmas cake,'' a sweet that no one would bother with the day after Christmas.

Now the average age for a woman's first marriage is 27.2 and rising. In 1980, when Japan's economy was growing vigorously, 80 percent of women age 28 were married. In 1995, 55 percent were. Today, 45 percent are.

Katsura Komami ought to be a catch. The 27-year-old executive at a giant automotive manufacturer is well-educated and attentive. She frequently travels abroad and enjoys musical theater and fashion. She wants a baby someday.

But like thousands of other ambitious women in Japan, Komami isn't thinking about marriage. She prefers to remain in the bedroom in her parents' modest apartment where she grew up.

Komami shyly acknowledges that she's a ``parasite single,'' a popular Japanese term for the more than 7 million unmarried Japanese women who live with mom and dad.

Nearly 90 percent of unmarried Japanese women in their 20s and 60 percent of single women in their late 30s still live with their parents, said Rieko Suzuki of Tokyo's Dentsu Institute for Human Studies, who's written a book explaining the nation's low birthrate.

``I feel like this is the only time I can enjoy my freedom, and use the money I earn on myself without obligations, without having to support others,'' Komami explained one night over pizza. ``Besides, the reality is if I got married, I'd have to choose between my career and a baby. Today, more women are choosing careers.''

Not many years ago, women couldn't support themselves outside marriage, as only low-paying jobs were open to them. Now many fret about losing their income and independence if they quit work and leave their parents.

Saving money at home

Professional women such as Komami who continue to live in their parents' homes -- where they usually make only token rent payments -- can take shopping trips to Paris or New York, go to fashionable restaurants and fill their closets with Louis Vuitton purses and Gucci accessories. They're Japan's biggest consumers.

A woman once ``had to get married in order to survive,'' said Suzuki, the researcher. ``But now, in order to live a better life, women choose not to marry.''

``You can have a much better life without getting married,'' said Masahiro Yamada, a sociology professor who coined the phrase ``parasite single'' to describe the phenomenon. ``There's a new term in the society called `wedding poverty,' '' Yamada said, because ``when you marry, you become poor.''

The rent or mortgage payment for a married couple is high, and the new couple typically goes from two incomes to one.

The cost of raising a child on a single salary also is prohibitive, said Mika Nemoto, a 26-year-old marketing executive who said she adored children. ``Public schools aren't good anymore, so you'd have to put them in a private school, and then there's cram school to consider.'' Cram schools are set up to help students pass competitive entrance exams to high school and college.

Japanese companies rarely offer a ``mommy track,'' a flexible work schedule to accommodate child care needs. Career women face the same demands as men to work long hours; during peak work periods, many don't get home before midnight. If they get pregnant, they often are forced to quit.

Husbands, however, still expect their wives to rush home and prepare dinner each night.

``We've discussed it, and my husband says he simply would not take paternity leave if we had a baby,'' said Mika Kuroiwa, who works in the programming department of a Tokyo television production company. ``So that settled it for me. It means we're not going to have children.''

``If we get pregnant, we're moving to Australia,'' said Yuki Takahashi, 29, whose Japanese husband studied for his law degree in Melbourne. ``I could never raise my child in a society as rigid as Japan.''

Dating is a chore

Just meeting a prospective partner can be an ordeal. Marriages traditionally were arranged between families, and while arranged marriages have gone out of style, many Japanese still aren't comfortable with U.S.-style dating.

Dr. Shigesato Takahashi, the chief researcher at the National Institute of Population and Social Science Research, said government data revealed that 49.8 percent of unmarried Japanese men ages 18 to 34 said they had no social relations -- no casual friendships, no dating relationships, no love affairs -- with anyone of the opposite sex. The comparable level for women is 41.9 percent.

``People who are trying so hard to pass university entrance exams, they actively suppress their desire to go out,'' Takahashi said.

Men spend long hours in the office and pass most evenings entertaining male clients or socializing with male colleagues or bosses. While Tokyo boasts more than 80,000 restaurants, men and women rarely dine together, except in the most romantic venues.

``I really don't have much opportunity to meet people,'' said Yuriko Hirose, 35, who studies tea ceremony and flower arranging and helps in her mother's floral business.

When Japanese men and women do meet, they have trouble talking to each other. ``The single men seem so helpless; they are really the parasites who depend on their mothers,'' Hirose said.

Sex counselors and therapists say men and women seldom discuss sex or feelings.

And marriage isn't the ticket to a good sex life. In Japan's only comprehensive study of sex lives, completed three years ago, one in five married couples in their 30s and 40s said they were ``sexless,'' meaning they have sex less than once a month.

``It's hard for Americans to believe,'' said Takao Sano of Mitsui Homes, one of the nation's largest home builders. ``But 40 percent of our customers ask us to separate the bedrooms'' between husband and wife. Often the couples are in their late 40s. Usually, Sano says, it's the wife who wants a separate room.