Sixteen years ago, Arlington housewife Alice Uehling found herself with grown children and her well-run home empty. Her husband had died, and she needed an occupation.

"As she looked back over her life," says friend and business associate Bonnie Gillespie, "she asked herself, 'What do I know how to do?' And she decided, 'I know how to be a mother.'"

From there, it was a short step into a position as "surrogate mother and homemaker" in a single-parent family after the death of a young mother. When that job ended, another came up, then another, and another, until Mrs. Uehling decided to establish an agency.

That was the impulse behind Mothers-in-Deed, a 9-year-old national firm that, along with a handful of agencies in the area, fills the gap when a parent is wrenched from the family.

"We get a lot of widow or divorce cases," says Gillespie, the East Coast branch manger, "and cases where one parent is an alcoholic, or mentally depressed."

The surrogate mother's role, as Moter-in-Deeder Joan Ashworth puts it, is "to be the stable influence between the children and the two disagreeing parents. These are cases where the parents have a lot on their minds, and the children need a strong sense of stability, since their lives are changing so."

The children, Gillespie admits, can be "unpleasant, at best." One of her cases was in a home where the mother had left to grapple with debilitating alcoholism, "and I was hired as Housekeeper No. 4 in as many weeks."

The house was chaotic, she says. "The kids didn't even know how to sort their clothes-everything was piled in heaps. The father was sad, the kids resented me, and many nights I drove home with tears streaming down my face."

She decided she was there to "restore a sense of peace and harmony -- to make the house a home," and started trying to work with the children. She did everything you would expect an at-home parent to do: drove them to Girl Scout meetings, baked cookies for the PTA, drew pictures for the children's classmates.

"When one of the children's classmates said, 'I wish my mom would come to school and draw like Bonnie's does,' that was a turning point -- the child could see that I cared."

She showed the children how to take care of their things, got the house back in running order (Mothers-in-deed does not include housekeeping, but the women do some "picking up" and get work going on schedule) and made dinner every night, sitting down with the family.

"After 10 months, everyone wanted to come home at night. The mother has since then rehabilitated, and now, we're all the best of friends."

Although Gillespie's work covered only afternoon and evening hours, many "mothers" work on a live-in basis and do "everything a grandmother would do," says "mother" Nan Croft. She works for a divorced Navy doctor, caring for his 5-year-old, doing the shopping and occasionally acting as the doctor's hostess.

"Of course, his friends are so much younger than I am," she says, "so I usually greet them and retire."

The agency tries to separate by age when making assignments, says Gillespie, "though some of our women have fallen in love with the daddies and gotten married."

Most Mothers-in-Deed are hired for single-parent families undergoing a crisis, "but we have expanded recently to take on two-parent families, where both adults work," says Gillespie. Their employes are usually displaced homemakers, though "we've had registered nurses, ballerinas and a probation officer take on the job."

The work, she concedes, is not for everyone. "For every 50 people we interview, only one makes a real surrogate mother." The interviews are hour-long affairs, followed by a check on "at least three references."

The one-out-of-50 "mother," says 8-year veteran Ashworth, should be prepared to "accept a totally different way of living. Everyone's home is unique."

When Ashworth (the widow of a British attache) was hired to run a single-parent family with a 14-year-old boy, she worked, "gingerly and quietly for three months, just trying to get the mother's things out of my bedroom."

When the father complained that his son never entertained friends in his own room, she decided "to peek in one day. There was one dresser. It was white, and had little ducks on it." That room was the next thing she tackled.

Other problems, however, are tougher than rearranging a living space, "and you have to turn them around gradually. Like poor health habits -- I bought a toothbrush and toothpaste for the son, and told him I expected him to use these things."

The son is now in the Marines, "and my boss' 93-year-old father has come to live with us!"

Ashworth says she likes being either a "daughter or a mother-in-deed." It's "an excellent situation for a widow. Women shouldn't live alone, I don't think. You get sloppy."

Besides, the job uses her talents. "I feel I've had some success in raising children. My own are doing very well. And if you did run a happy home for many years, you feel you could do it again.

"I've never," she says, "worked a day in my life."