Almost every afternoon at Smyk, a large children's store in downtown Warsaw, a line of pregnant women forms in front of a counter on the second floor where supplies for babies are sold.

Each woman shows a clerk a card certifying pregnancy, and in return is handed a red plastic basket containing pajamas, T-shirts, sweaters, bibs, blankets and small cotton towels. The basket is not a gift. Buying everything in it could cost a prospective mother the equivalent of three or four months of a typical salary.

Neverthless, these women are enjoying a kind of special treat: for this is their one and only guaranteed opportunity to buy some of the most sought-after goods in Poland, baby clothes, for zlotys. Once they take the items they want from one basket -- up to four pajamas, four shirts, two sweaters and two towels, among other things -- their "pregnancy card" is stamped and they are not allowed to purchase the rationed items again.

Unless, of course, they have another child.

"It's improved since the last time I was pregnant, during martial law" four years ago, said one young woman waiting in line on a recent afternoon. "Then they had almost nothing, and what they had was so ugly I bought almost nothing at all."

The line at Smyk is just one of the peculiar customs pregnant women in Poland have come to accept as normal in recent years. Unlike most of the rest of Europe, this nation of 37 million is experiencing a baby boom, and state-provided services, from maternity wards to bib manufacturing, have not kept up.

The result is not only inconvenience. In the last year, poor hygiene and supplies have caused the deaths of groups of newborn babies in hospital maternity wards at least twice, with a total of 14 dead. Many women complain about less serious infections picked up by their infants at the hospital and about crowded maternity wards where doctors' visits, sanitary materials and even clean sheets can only be obtained with bribes.

"It's a disaster," said Jerzy Holzer, director of the Institute of Statisics and Demography at Warsaw's state School of Planning. "We demographers reported at least 10 or 15 years ago that another wave of children was approaching and that investments in services were needed. But nothing was done."

The boom of births began in 1982 and peaked in 1983, when a record 720,000 babies were born. Since then, the numbers have declined, with an estimated 675,000 births in 1985. Demographers, however, said Poland continues to have one of the highest rates of population growth in Europe, trailing only Ireland, Iceland and Albania.

Holzer said the high number of births in recent years is an "echo" of the huge baby boom Poland experienced after World War II, culminating in the mid-1950s. Like their parents, the current wave of children will form a "population wave" in society that will soon strain schools, housing and eventually, the job market, he said.

Some Polish observers maintained that the country's political crises in the late 1970s, culminating in the independent trade union Solidarity in 1980, can be largely attributed to the frustrations of the first baby boom generation. While Holzer dismissed that argument as simplistic, he said government leaders are worried about the crises the next population wave may bring.

"There's no doubt that our increase is so high that it creates several economic barricades," he said. "It makes everything harder."

At the moment, the greatest hardships seem to be borne largely by the mothers of the new generation. For many Polish women, the shortages of goods and services during pregnancy are matched by the regimented procedures of hard-pressed maternity clinics.

For most, the state's role in a baby's birth begins when a doctor, usually the one who confirms the pregnancy, presents a woman with a "Card of Pregnancy in Course," to be carried at all times. This document records a woman's visits to her physician during pregnancy and allows her various privileges, such as the one-time shopping spree at the Smyk store.

Pregnancy cards also allow women to move to the head of Poland's ever-present shop lines, but only on weekdays.

"At 3 p.m. on Friday I stop being pregnant," one 25-year-old Warsaw woman in her first pregnancy complained. "Maybe the authorities don't think pregnant women should go out on weekends."

The regulations multiply once pregnant women enter the hospital for deliveries. All are required to remain in maternity wards for at least five days, the day of the delivery plus four 24-hour periods afterward, regardless of their condition or wishes.

During this time, mothers may see and hold their children only if they are nursing them. Once they agree to nurse, they must do so seven times a day, exactly every three hours, without exception. No flowers, gifts, visitors or incoming telephone calls are allowed at most clinics.

In theory, at least, fathers may not attend the birth, and must wait four days to see their new child. They may not even learn the baby's sex unless the mother can gain use of a phone or smuggle out a letter, because in some clinics officials will not reveal the sex of newborns to callers in order to avoid embarrassing mistakes.

Predictably, such regulations have encouraged some extraordinary practices that have become part of the custom of childbirths here. When a pregnant woman enters the hospital, for example, families and friends assemble neat, inconspicuous packages of juices, chocolate and other treats that can be smuggled into wards by porters or nurses who carry out such favors in exchange for tips.

Some anxious fathers try to smuggle themselves in for a peek at their babies. Others assemble outside the clinic and attempt to hold shouted conversations with their wives through the windows.

Doctors say the mandatory four-day stays are intended to allow for the treatment of newborns with antibiotics, while other rules are forced by the harried pace and overcrowding of wards. In some clinics, delivery rooms can be packed with six or seven women at a time attended by a single doctor.

Although all maternity services are nominally free, having money to spend on a pregnancy can make an enormous difference.

"If you want any service at all, you have to pay," said a 30-year-old Warsaw secretary who recently gave birth. "Otherwise you can't even get a clean gown," in the hospital.

Women usually pay doctors the equivalent of $5 for each visit during their pregnancy and hand substantial daily tips to nurses, orderlies and cleaning women once they enter the hospital.

Even the shortage of baby clothes can be overcome by the affluent. Since April of this year, Poles with access to U.S. dollars and other western currencies have been able to purchase high quality clothes, toys and other supplies at a store inconspicuously tucked above a grocery in the city center.

A joint venture between the state trading firm Baltona and the Austrian Harris Co., the store, called For Mother and Child, offers cotton pajamas for $20, child-sized jeans for $32 and baby carriages for $200. Although the average Polish monthly salary is worth less than $40 on the local black market, the readiest source of hard currency, the shop is often crowded with Poles, according to manager Maja Gabric.

"What we have here is the middle class and the upper class goods," she said. "We do not have the cheap things. That is the decision of our Polish partners."