Today, Dec. 19, isn't exactly Katie Beckett's birthday, but for the last three years, it's been a day of celebration for the Beckett family and it will be again today.

It is the third anniversary of the day Mary Katherine Beckett (and her tubes and her breathing equipment) came home from the hospital.

It is the third anniversary of the day Julianne Beckett says her life began.

You remember Katie Beckett. She's the baby who was on a respirator in a Cedar Rapids, Iowa, hospital for nearly three years. Her parents wanted to take her home and the doctors and the nurses said they thought it could work out. But because of a glitch in the Medicaid system, the Becketts would lose the government assistance that was paying some $12,000 a month while their child was in the hospital. Home care would have been only about $2,000, but the way the law was written, once Katie came home, the money would stop. Any money.

The Becketts couldn't afford to bring their baby home, and the taxpayers were putting out $10,000 a month more than they needed to.

Then their plight became known. The Becketts' congressman, Thomas J. Tauke, Vice President Bush and finally President Reagan intervened to activate what is now called the "Katie Beckett Waiver."

Katie came home, but, says Julie Beckett with, even now, a catch in her voice, "but, oh, I never had my baby . . . I'd have just liked to have had my baby . . ."

Katie was born on March 9, 1978, a 2-pound-plus preemie who, nevertheless, did very well, better than most in her weight class. But at five months, Katie developed viral encephalitis that left her unable to breath or eat or drink unassisted.

For months, her survival was in doubt.

Then, it appeared, she would live, but not without a tracheostomy for breathing and a gastrostomy for feeding.

Additionally, she needed breathing help from a ventilator. Pneumonia was a constant threat.

Still, the Becketts wanted their baby home.

Julianne Beckett, 35, known mostly as Julie, was in town recently to address about 500 health-care professionals concerned with the group of children Beckett refers to as "medically fragile."

She is in great demand as a speaker, especially to health professionals, because of the seemingly miraculous strides Katie Beckett has made since her homecoming. Because, although it is still true that Katie is dependent on her equipment, it is also true that she is growing, behaving, learning much like any other child her age. The medical world is discovering that no matter how much sensitivity and caring is provided in a hospital, there is an indefinable, essential but inimitable quality to home care. Katie Beckett is their principal prototype.

After her talk, Julie Beckett concedes that she is mainly "Katie Beckett's mom," something she is happy to be. But she is also a social studies teacher at a Cedar Rapids Junior High School and an active member of a rapidly growing support organization called SKIP for "Sick Kids (Need) Involved People." For the past year or so she has been on a regular lecture circuit, educating all who will listen to the need for near-as-possible normal family life for youngsters dependent, one way or another, on medicine's new life-giving technology.

But wherever she is, she says, "I keep my watch on Iowa time so I can follow Katie's schedule exactly, even when someone else is taking care of her. As long as the players I have put together for her do their job, she'll be just fine. But I still need the time to get away, to be Julie Beckett, not just Katie Beckett's mother, even though that role has given me the greatest pleasure in my life."

Even at the beginning, when Katie required up to 18 hours a day on the ventilator and near-constant attention to preventing a blockage of the tracheostomy or gastrostomy, Julie Beckett continued to work. If she needed to, she says, she brought Katie to school with her. "There I'd be," she says, "lecturing about the Romans and feeding Katie through the gastrostomy. Those kids really got an education."

After Katie Beckett went home, the Department of Health and Human Services formed a board to review cases where an exemption from Medicaid restrictions might be warranted. It quickly became known as the Katie Beckett review board and has now granted 115 waivers, with about 30 pending. Its mandate expires at the end of this year, however. States are now authorized to establish similar programs and about two dozen have already established programs.

"I'm not a Democrat. I'm not a Republican. I'm just a mom," says Beckett. "But President Reagan has been very supportive to our kinds of kids . . . And do you know what he said when he saw Katie last year? He picked her up and hugged her and there were tears in his eyes and there were tears in my eyes and my husband's eyes and the president said, 'This is the happiest thing I've done in my presidency.' "

The sums involved may or may not be vast, but Julie Beckett is certain that there are families "out there, isolated, struggling" to care for this new generation of technology-dependent children. "That is what SKIP is for," says Beckett, "to find them and help them get help . . . even to give them somebody to tell things like 'this kid is driving me nuts,' somebody who will understand. After all, you find that in any family -- you know, the 'Calgon-take-me-away' syndrome." By mid-1985 there should be a SKIP chapter in every state, says Beckett. SKIP's national headquarters is in Severna Park, Md.

Katie Beckett is "something of a miracle," Julie Beckett says casually. From the tube-bound toddler the Becketts finally brought home in December 1981, Katie has developed into a leggy first-grader, about 3 feet 2 inches tall and weighing about 50 pounds. These days she is suggesting to her parents that a baby brother might be fun.

She now requires the ventilator only when she is asleep -- about seven hours a day -- and she takes some soft foods and some liquids by mouth. She is mainstreamed in a Cedar Rapids first grade that has "regular -- you know, regular kids," says Beckett; as a result, she believes, Katie is speaking clearly -- although she still needs and gets speech therapy. She is at grade level or above in her schoolwork.

The coming-home anniversary party is at the Becketts'. The doctors and nurses from St. Luke's Methodist Hospital pediatrics unit will be there. It is as much for them as for Mark Beckett, a lumber wholesaler, and Julie and Katie Beckett. "But," says Julie Beckett, "they are coming to my house. I went to their house for three years, and now they're coming to mine."