WASHINGTON (AP) - Gene testing is going mainstream: Starting this month, tens of thousands of white Americans will be offered testing to see if they carry a gene mutation that causes cystic fibrosis even if no one in their family has the disease.

Under new guidelines, obstetricians and gynecologists are supposed to offer the gene test to every Caucasian - or the partner of a Caucasian - who is pregnant or considering having a baby.

It marks the first time gene tests are being offered to the general population. Until now, they have been recommended just for small groups of people who know they're at high risk for a particular inherited disease, such as when an illness runs in the family.

Are we ready for mainstream gene tests? The American College of Obstetricians and Gynecologists is betting that with a little education, Americans will be savvy enough medical consumers that the screening will prove a boon.

To help expectant couples decide whether to accept the test, the group has prepared easy-to-understand educational pamphlets - available from your doctor - explaining cystic fibrosis, how gene testing works, and the relevance of parents-to-be discovering they have the gene mutations that cause it.

Babies must inherit a bad gene from both parents to have the disease, so if the mother has a mutation, the dad must be tested, too.

"It's something patients have to decide - do they want it or not," stresses Dr. Michael Mennuti of the University of Pennsylvania, who co-authored the testing guidelines.

About 30,000 American children and young adults are living with cystic fibrosis. It attacks their lungs, clogging them with a thick mucus, and can harm digestion and vitamin absorption by clogging the pancreas and intestines.

Treatment has improved in recent years, lengthening life span. Still, patients typically die in their 30s, most from lung damage or infection.

Why test so many parents? While it can affect anybody, cystic fibrosis is the most common inherited disease among Caucasians. People can carry the defective gene without knowing it - more than 10 million Americans do, including one in every 29 whites.

But because there are so many unsuspecting carriers, most babies with the disease are born into families that didn't know they were at risk. If both parents harbor the defective gene, they have a one-in-four chance of having a baby with the incurable disease.

"The vast majority of couples will get reassuring news," that they aren't carriers, notes Dr. Francis Collins of the National Institutes of Health, who co-discovered the gene in 1989.

Testing is best done before a woman gets pregnant, he says. If both parents are carriers, they might opt for in vitro fertilization, for instance, where the resulting embryos can be tested for the disease and only healthy ones are implanted into the mother's uterus.

If parents learn they are carriers early in pregnancy, the fetus can be tested. If the fetus does have it, abortion is one option - but many such parents do as patients of Dr. Debra Baseman recently did: They spent the months of pregnancy learning about top-notch care and lining up specialists for their child. Very early care, especially nutritional care, keeps many patients healthier longer.

Parents often say, "the medications are good, the life span is longer, and who knows what medications will be around in 5 or 10 years," said Baseman, a Princeton, N.J., obstetrician who has offered routine screening for cystic fibrosis for several years and says about three-fourths of her patients accept it.

The guidelines say the test should not be restricted to Caucasians. While they are the main target because of their higher risk, the test should be available to anyone who wants it. One in 46 Hispanics carry the bad gene, as do one in 62 blacks and one in 90 Asian Americans.

A test typically costs about $265; doctors say many insurers do pay for it.

The test is good but not 100 percent accurate. There are about 1,000 known mutations in the gene that causes it, and the new guidelines advise test laboratories to check for a minimum of the 25 most common. Genzyme Corp., the largest test provider, typically tests for 87 mutations.

How well this widespread gene testing works will influence how other gene tests are introduced to Americans.

"It will be very important to see how this goes," Collins says. "Certainly it requires the obstetricians to become more familiar with genetics than many of them have previously had occasion to do."

Copyright 2001 The Associated Press. All rights reserved.