PITTSBURGH (AP) _ Lois Jones holds her breath every time her 7-year-old daughter, Stormie, scrambles onto the playground monkey bars. She is anxious when the child gets a simple case of sniffles.

Such everyday trials of childhood are serious business when they involve the world's first recipient of a transplanted heart and liver.

Shy, blonde Stormie Jones underwent the historic operation Feb. 14, 1984, and one year later, everyone says she couldn't be better.

''She does everything now. She scares me,'' Mrs. Jones, 28, said. ''I put it (the transplant) in the back of my mind - until Stormie gets a fever. Then it pops up.''

But, time after time, Stormie proves to her mother and her doctors that she is made of sturdier stuff.

''That little tiger. ... We worry about her, and probably all that worry is not justified. She always does fine,'' said Dr. Cara East, one of Stormie's physicians at the University of Texas Health Science Center at Dallas.

''I'm fine,'' Stormie said matter-of-factly in a recent telephone interview from Dallas, where she now lives with her mother and 10-year-old sister, Misty.

Misty agrees - and acts like any older sister.

''We fight a lot. Ask my mom. She (Stormie) takes my stuff sometimes,'' Misty said, quickly listing her roller skates and a favorite doll as examples.

More than a year ago, Mrs. Jones contacted the Children's Hospital of Pittsburgh, where experts decided the dying child's last resort would be the world's first simultaneous heart-liver transplant.

Stormie suffered from a rare congenital disease that had increased the cholesterol in her blood to nearly 10 times the normal level. Misty suffers a less serious cholesterol problem that is treated by diet.

Because of the chemical imbalance, caused by a faulty liver, Stormie had suffered two heart attacks, undergone two unsuccessful triple-coronary bypasses and had a valve in her heart replaced.

The 16-hour procedure, led by Dr. Thomas E. Starzl, a pioneer in kidney, liver and pancreas transplants, and heart transplant surgeon Dr. Henry Bahnson, was hailed as a medical milestone. By replacing the young patient's misfunctioning liver and her damaged heart, surgeons instantly bettered her chances for life.

Stormie returned home to Texas last May and, following a quiet summer, started first grade at Casa View Elementary School, just a few blocks from the modest frame home the family rents.

She has improved day by day, despite colds and fevers that caused her to miss four of the first six weeks of school.

''She's great. She's normal. She's living a normal life,'' Starzl said.

Her dramatic progress, in fact, paved the way for a second heart-liver transplant Nov. 9, but 2-year-old Kellie Cochran of Birmingham, Ala., died when her new liver failed three days later.

Doctors say a third such operation is tentatively planned early this year for Mary Cheatham, 17, of Fort Worth, Texas, who suffers from the same cholesterol disorder as Stormie.

The double transplant ''holds out some hope for individuals who can't have their cholesterol controlled by any other means,'' according to Dr. David W. Bilheimer, associate dean for clinical affairs at the Health Science Center in Dallas.

''It's very effective treatment, but it's also very heroic and it carries its own problems with it,'' Bilheimer said. ''You have to balance those risks of the operation and the possibility of rejection versus control of the cholesterol.''

Every morning and night, Stormie takes at least five kinds of medicine, including aspirin, to prevent her body from rejecting the transplanted organs and to keep her blood pressure down. She will have to take the anti-rejection medication all her life.

Every Monday, Stormie and her mother make the 45-minute trip across Dallas to the Health Science Center for blood tests. The child's cholesterol level is still twice as high as normal, and doctors are awaiting approval from the federal Food and Drug Administration for an experimental treatment now used only on adults.

Misty and Stormie are restricted to a low-fat, low-cholesterol diet consisting primarily of vegetables and pudding made from skim milk.

Perhaps the greatest adjustment for Stormie has been school.

Her teacher, Ann Dunaway, treats her no differently than the 25 other youngsters in the class, but she was forced to explain Stormie's background to her pupils when reporters and photographers invaded the class.

''I told them that Stormie had had some surgery that not anybody else had had. So she's special in that way,'' Ms. Dunaway said.

Stormie sometimes makes up excuses to stay home because of taunting from other youngsters. But her mother, concerned her daughter might become spoiled, refuses to give in.

''One little boy asked her if she was Stormie Jones. When she told him yes, he said, 'Well, you're going to die,''' Mrs. Jones said.

''She gets depressed about it from time to time. She kind of gets the impression that she's getting picked on. But when something good happens, she thinks, 'Wow, I am special,''' she said.

Despite her growing ease around reporters and other strangers, Stormie still won't talk about her transplant.

''Basically she doesn't talk about stuff like that unless we're around people and somebody tells about their surgery,'' Mrs. Jones said. ''Then she'll say, 'I remember that. That hurts.'''

The attention has had its benefits. The family still receives gifts and letters of support from well-wishers around the country. On Christmas, dozens of gifts, even a tree, came from people the Joneses didn't know.

''We probably wouldn't have made it, except for the public. There's good people out there who realized the expense of everything, who helped us through the whole situation with donations and just moral support,'' Mrs. Jones, a divorcee who recently found a job repairing gas stoves.

So far, most of Stormie's medical expenses have been covered by the insurance of her father, an itinerant oil driller. Contributions pay for almost all the rest.

Mrs. Jones said she looked to the future with optimism.

''We made it, and we'll make it through another one,'' she said. ''I'm really very thankful because this year marks another year that I've had to spend with Stormie. And that truly is a miracle.''