DON WALLACE KNOWS better than to dry a baby's bare behind with a hot air blower.

In four years as a househusband--a word he hates for its "Phil Donahue-ness," but uses for lack of a better term--the 32-year-old father of a son and a daughter has never toasted a cheese sandwich with a steam iron, wrestled a frenzied washing machine, threatened his wife's boss with a chain saw or suffered terminal humiliation over buying Maxi-Pads.

So each time actor Michael Keaton took those slapstick tacks to bringing up babies in the new movie "Mr. Mom" at Thursday night's preview showing, the 6-foot-3, bushy-bearded Wallace sunk lower and lower in his seat.

"I just hope that most people will realize this movie is about as realistic as an 'I Love Lucy' rerun," Wallace whispered as Keaton fled from "Jaws"--a vaccuum cleaner run amok. "The guy has to be a total idiot to have three kids and not know how to make popcorn, use a washing machine or an iron. I don't think it does a helluva lot for the image of the American male."

Image is something Wallace frankly hasn't cared about much since he and his wife Laure decided on their domestic arrangement five years ago. He is one of an estimated "several thousand American men who have primary child-care responsibility," according to educator and househusband Michael Robinson, associate editor of Nurturing News: A Quarterly Forum for Nurturing Men.

Both Wallaces are native Washingtonians--he graduated from the District's Archibishop Carroll High School in 1969 and she from Northwood High School in Silver Spring the same year. They met in Geology 101 at the University of Maryland and married in 1974.

"When we decided to have a baby in late 1978, Laure had been working with the U.S. Geological Survey for several years and was making the bulk of the salary," Wallace said Thursday afternoon in the living room of the family's rented Falls Church home. "I've got my degree in drama, which isn't very marketable, so I'd kind of hacked around with several jobs--house painting, managing a record store. I started my own business refinishing antique furniture in 1976.

"Laure was enjoying her career, and I had the flexibility of scaling back my hours so I could stay home with the kids. We never really considered day-care because we wanted the children raised in a loving home with a family member. To us it seems logical for Laure to keep her secure government job while I stay home with Jesse aged 4 and Corey aged 1 ."

Over the years the Wallaces have honed their schedules to allow as much sharing of family responsibilities as possible. Laure Wallace works Monday through Thursday for the Interior Department's Minerals Management Service. Don Wallace spends a few hours each evening and all day Friday working on furniture. She cooks dinner, he cleans. She does the lawn, he does the laundry.

The most remarkable part of the arrangement, said Wallace as he casually unpinned Corey's diaper and inserted a thermometer into her rosy rump ("She's felt a little hot all day") is that "other people think it's so remarkable.

"It's 1983, for pete's sake. With all the social upheaval we've been through, what's the big deal?

"I don't want to sound like some Alan Alda liberal, but Laure is as good a breadwinner as any man, and I'm as good a childraiser as any woman. We have no predefined expectations about what we should and shouldn't do because of our gender."

For all the lip service paid toward changing roles of men and women, he said, "what it amounts to is women going out into the work force. Men are doing very little to penetrate the woman's world.

"I don't mean to stand on a soapbox about it or put down choices anyone else makes, but any man who has the attitude that some things are 'women's work,' and he'd never do any of it, makes me feel very sorry for him. He doesn't know what he's missing."

Wallace bent his tall frame over the wiggling infant, who gazed adoringly into his eyes, as he repinned the diaper. "Sure the kids get cranky, and I sometimes feel like bouncing off the walls. But then they'll say or do some little thing that absolutely delights you. Like the time Jesse was 13 months old, driving in the car with me, and out of nowhere he said 'bulldozer' when we passed a construction site. The fulfillment is indescribable."

Just then, Tasha the Wolfdog started barking, Corey started crawling toward the door and Jesse ran outside hollering, "Mommy's home, Mommy's home." Slightly disheveled from a long day of "analyzing rock units," Laure Wallace opened the door with her son in one arm and a quart of milk in the other.

"Good, you remembered the milk," Don Wallace said, kissing his wife and placing the baby in her arms. " Corey has a little fever. I didn't tell you because I didn't want you to worry."

The reason few couples do what they are doing, Laure Wallace said, after kicking off her shoes and settling in the living room, is that "few men feel comfortable having their wife earn the paycheck.

"And I think a lot of women don't want to give up control of the home. At first I felt a certain amount of guilt at not staying home with the kids. But I really enjoy the stimulus of working. Sometimes it would be nice not to have the hassles, and I still go through periods of feeling I'm missing out.

"I was on a business trip in Denver when Jesse said his first word 'whazzat' , and Don was the first one to see him walk. But if I was home, then Don would miss out. This just seems very natural to us."

Their parents--who had traditional roles--are supportive. "We could have been upwardly mobile with a house and new cars and day care," Laure Wallace said. "Or we could get by on $20,000 a year with used cars and a rented home and a more satisfying family life. There are trade-offs, naturally. It would be nice to have the security of money in the bank. But it really wasn't a hard choice for us."

The Wallaces weren't always this blase' about their life style. "I felt a little defensive at first," Don Wallace admitted. "When I take the kids to the grocery store in the middle of the day and everyone else is a housewife, I get stared at. That used to bother me. Now I don't even notice it.

"And I remember one time we went with Laure on a business trip and stayed in the motel when she went to her meetings. Jesse was being fussy and this lady came up to me and said, 'Oh you poor man left alone with a baby! Can I help?' I got rather testy and said, 'No thank you, I'm in control of the situation.' I felt the implication was that I was some kind of helpless idiot."

In April the Wallaces tried taking the kids to day-care so Don could build up his business. "That didn't last long," he said. "Jesse was miserable, and we were, too. I can't tell you how awful I felt dropping him off and driving away."

Life with father, asserted their sandy-haired 4-year-old, is "lotsa fun. He makes me lunch. He takes me in the car." Does Jesse feel different than his friends? "Uh-uh." Who stays home with his friends during the day? "The daddies."

Don Wallace's aversion for "predictable, slapstick movies that center on something trendy" would probably have kept them from seeing "Mr. Mom," had they not been asked to offer their expert opinion.

"I was hoping they would take the opportunity to show a father getting close to his children," Don Wallace said after the show. "But they didn't explore characters at all. They used the role reversal simply as a convention to anchor gags you've seen on TV a million times. There was very little depth."

"The wife didn't seem to miss the kids at all or experience any conflict about going to work," Laure Wallace said. "It was funny in places, but not very believable."

On a scale of 1 to 10, the Wallaces gave "Mr. Mom" a 5 for comedy. For realism, Don Wallace said with a grimace, "I wouldn't even put it on a scale."

Take, for example, Mr. Mom's regular poker game with "the girls" for cents-off coupons ("I'll see your Extra-Protection Ban Roll-On and raise you one New Improved Cool Whip.")

"Women don't like to let men into their circle," he maintained. "When we lived in Olney, a neighbor came by to invite Laure to the Wednesday afternoon mother's coffee klatch. When Laure told the woman that she worked Wednesday and I was home with the kids, the neighbor said, 'Oh, too bad.' She didn't even think to invite me."

The movie's major flaw, he said, was that "they focused only on the drudgery and showed none of the joy.

"They concentrated on whether he could handle the washing machine instead of whether he could raise a good child. In the one serious interaction he has with his son, over the kid's security blanket, he goes for gags the kid couldn't understand. They threw away a potentially great scene for a cheap guffaw.

"You never got a feel for what he learned from the experience or how he changed as a father. It's thrilling to be a part of the daily development of a child, and they showed none of that. Basically, they blew a great opportunity."