At least once a day, Patricia Devlin puts a "Do Not Disturb" sign on her office door, secures it with a lock she had specially installed, and switches her mind off her job as deputy director of consumer affairs for Fairfax County. She then takes up to 30 minutes to pump milk from her breasts and store it in a small cooler of ice for her baby's meal the next day. During this time, to relax so her milk will flow, she must tune out her job and tune in thoughts of her baby.

Devlin, who nursed her first two children for 2 1/2 years each and who is now breast-feeding her third child, is one of a growing number of women who have found that working and breast-feeding can be compatible.

"The logistics are hard," she admits. "But as a working mother I think it's even more important to be nursing because I don't have that skin contact during the day as if I were at home . . . I never thought that I wouldn't continue to breast-feed. It seemed the right thing to do and the natural thing to do."

Today, more than half of all U.S. mothers breast-feed their infants upon birth and more than 26 percent of breast-fed infants are still nursing after six months. More than half of all mothers of children under 6 are in the labor force.

The American Academy of Pediatricians endorses breast-feeding exclusively for the first six months of life, yet standard maternity leave is about six weeks -- not enough time for a woman's milk production to adjust to long stretches away from the baby.

Many women believe so strongly in the nutritional benefits of breast-feeding that they are willing to pump and store milk in unfamiliar and uncomfortable rest rooms and lounges, lug around equipment and storage containers, tolerate sometimes embarrassing questions and comments from coworkers and wrestle with never-ending fatigue.

"We need to help working mothers who breast-feed be prepared for the stress they will face," says sociologist Kathleen Auerbach, a lactation consultant at the University of Nebraska Medical Center. "We expect them to be mothers, but publicly we don't give them the support because it's not looked at as 'professional.' "

In a recent study of 567 working and breast-feeding mothers, Auerbach heard dozens of stories about uncooperative employers. One hospital supervisor wouldn't let a nurse store her just-pumped milk in the employes' refrigerator because he said the breast milk would take space away from those who wanted to use it for "legitimate" reasons. One secretary was prohibited from taking coffee breaks because she was using her break to pump milk and not to drink coffee.

The biggest problem faced by mothers who work and breast-feed, Auerbach says, is fatigue. Breast-feeding or not, a working mother finds that she has too little time to perform all the roles she's expected to play -- mother, housekeeper, cook, wife, professional. Therefore it's important for the breast-feeding mother to set priorities in her life so that she'll have time to nurse, rest and take care of herself, says Auerbach. The working mother who is well informed about the problems she may face -- fatigue, infections, sore nipples -- will be better able to adjust to new situations.

And in many cases, employed, breast-feeding mothers must use a little ingenuity to balance nursing with work.

For instance, one woman could not relax while pumping her milk because she was nervous that someone would disregard her "Do Not Disturb" sign and walk into her office. She now hides behind several tall boxes piled on the front of her desk.

A female factory worker who had no private place to pump her milk sought aid from a male colleague, who brought a blanket to work, constructed a makeshift "nursing cubicle" in the corner of a stairwell and stood guard while she pumped.

Working and breast-feeding is most difficult for a mother who returns to a full-time job before her child is four months old, Auerbach says. This mother is most at risk of fatigue, infection, engorgement and leakage.

Auerbach offers this advice:

* Simplify your life. Since the infant must be nursed at least every three hours (including through the night) when the mother is home, the first priority is rest.

* Plan ahead. A pregnant woman who wants to continue to nurse after she returns to work should talk to her employer about the length of maternity leave and working options, such as part-time hours and working from home.

* Decide how you are going to pump. Hand pumps, preferably the nonbreakable, cylindrical models, are recommended and can be just as efficient as electric pumps. Health care practitioners warn against cheap pumps that can harm a woman's nipple. Some women can efficiently hand-express their milk without a pump.

* Consider where to store the milk. Breast milk must be kept cool at all times. If no refrigerator is available, an insulated Thermos or small cooler will suffice.

* Decide where to pump. Look for a quiet and private place.

* Understand how often to pump. The rule of thumb: At least once every three hours for mothers of babies under four months, and every four to five hours when the baby is four to nine months.

* Consider how to find the time to pump. Twenty to 30 minutes of uninterrupted time is essential for mothers who are planning to store their milk. To simply relieve breast fullness, a few minutes should suffice.

* Plan a supportive day-care arrangement. The babysitter must know how to handle fresh or frozen breast milk and must cooperate with the mother in planning a schedule for the child. The babysitter must understand that a breast-fed baby behaves differently than a bottle-fed baby. The breast-fed baby is much more conscious of who his or her mother is, may reject the bottle, may require more frequent, but small, feedings, and may demand more bodily contact.

Remember the importance of rest and nutrition. The nursing mother, working or not, must find time to drink plenty of fluids, eat nutritious foods and rest. She is producing about a quart of milk a day when the baby is an infant. Nursing requires 500 more calories a day than pregnancy. This means that meals may not be skipped, junk food should be kept to a minimum, a glass of water or juice and snacks should be kept at the desk, and those few extra pounds may not come off immediately.