Three years ago, Julie and Michael McCalpin had the foresight to circle their magic date: April 9, 1999.

Long before they married, or even so much as picked out a china pattern, the couple had staked out their reproductive future.

In two weeks, the McCalpins will spend what could be politely termed as "quality time" together to fulfill their long-held goal: conceive a "Millennium Baby," a little Y2K bug of their own.

"It's a unique opportunity that few people have ever had," said Julie McCalpin, 28, who spends the balance of her day restoring a 90-year-old home in suburban Portland, Ore. "When Mike and I first started getting serious, we knew we wanted children, and we saw this date coming up and we thought we should be ready to go."

The McCalpins are hardly alone. Around the world, couples are gearing up for what could become the greatest concentrated effort at human procreation the planet has ever experienced -- or not, as the case may be.

This much is certain: If you want to have a baby on Jan. 1, the window of opportunity officially opens today.

"I just think it would be a really good start for a child, a new beginning," said Jacquie Craig, 34, a Denver mother of three who wants her fourth to have a 1-1-00 birth date. "It's worth the effort."

Like the McCalpins, the Craigs have been researching the hows and whens of having a Y2K baby by surfing the Internet. Various sites in cyberspace tout calendars and free advice on how to time a pregnancy.

Even warnings that hospitals may not be the ideal place to be on Jan. 1 -- if predictions that Y2K computer glitches will cause blackouts and equipment failures are to be believed -- have not deterred couples.

"Somebody has to be born on that date," said Mrs. McCalpin.

For women with well-timed biological clocks, April 9 is generally recognized as the zero hour -- it's precisely 38 weeks before Jan. 1. That's the average length of a human gestation.

Unfortunately, even for the lucky women with fortuitous internal timing, there are no guarantees of success, noted Dr. Eugene Katz, director of the Greater Baltimore Medical Center's Fertility Center.

Only an estimated 5 percent of women deliver on their due date, and a "normal" pregnancy can last anywhere between 36 and 40 weeks, Katz said.

Add to that the fact that a couple's chances of getting pregnant in any given month are only about 1-in-4 (worse for women over age 30), and the odds are definitely working against them.

"It's not likely," said Katz. "And I'm not sure I see the point of it."

In fact, Katz and other health professionals see efforts to precisely time a baby's birth as the latest evidence that couples today have some pretty unrealistic expectations about having babies.

"These days, you see a lot more people -- typically professional couples -- trying to plan a pregnancy, and then real life takes over," said Carolyn Gegor, a midwife at the University of Maryland School of Medicine. "They find out that even a two- or three-month window is hard to hit."

Such skepticism seems to have fallen on deaf ears. Some radio stations have launched Millennium Baby promotions, offering to put up couples in hotel rooms on April 9 and then track the results.

A Canadian company has snatched up the rights to the name "Official Millennium Baby," and is touting $2 million in cash and prizes for the first North American baby of the new year. One San Diego couple is raising money to have the ultimate millennium love child: Their goal is to have it delivered one second past midnight on Jan. 1 by Caesarean section on a tiny South Pacific island on the international dateline.

For more conventional couples, BabyCenter Inc., a Web-based retailer of products and information for expectant parents, is selling a $50 millennium baby "kit" that includes a fertility book, ovulation detectors, a pregnancy test, candles and massage oil.

More than 5,000 people have considered buying the product, said Lara Hoyem, a company spokeswoman. "It's been so popular we plan to offer the kit permanently."

Like many other Web sites, BabyCenter has also been offering tips to improve couples' odds. They include: "Number 3. Women should try to have an orgasm," and "Number 6. Keep stress under control."

Katz said he is generally unimpressed with such advice. The difference these things can make is "marginal" at best, he said.

But like the lottery, some of the people who play the millennial baby game are bound to win. If millions of couples attempt it, probability suggests that tens of thousands are going to succeed.

Erica and Aaron Maria, residents of suburban Seattle, want to be one of the sweepstakes winners. They decided in February that since they wanted a baby anyway, they may as well aim for the big day and just hope for the best.

"It just so happens this may be the month," said Erica Maria, who already has a 21-month-old daughter born on the July 4 holiday. "Maybe we're just an eventful family."

Putting Mother Nature on the clock

On average, a woman trying to conceive has a 1-in-4 chance of getting pregnant each month. Ovulation takes place roughly 14 days after the first day of menstruaion. To increase odds, conception generally must occur within a three-day period before or during ovulation.

40 weeks -- Today -- A "normal" pregnancy last 36 to 40 weeks being the average. Pregnancies, of course, can last longer or end sooner than that. Today opens the window to conceive a baby for delivery of Jan. 1, 2000, if there's a 40-week gestation period.

38 weeks -- April 9 -- This is the key day for an average gestation period -- it's 38 weeks from Jan. 1.

36 weeks -- April 23 -- This is 36 weeks from Jan. 1. Pub Date: 3/26/99