Before you call a repairman to fix your dryer, check to see if it's plugged in. A good 25 percent of the repairs made by those who service appliances are simply ''plug-ins,'' says Kay Keating, a home repair expert who wants consumers to avoid unnecessary service calls.
Mrs. Keating has taken her ''fixitips'' to national magazines, classrooms, newspapers, hardware stores, and congressmen's wives for the past nine years, after a lifetime of tinkering. The daughter of an electrical engineer, she says some of her most vivid memories are of the acres of wires she saw at the Western Union plant where her father worked to keep the lines open to the White House just before World War II.
''We were the go-fers,'' she says of herself and her brothers, adding that ''it was expected that when either of our parents took on a project, one of us kids would be there to help.''
Still, Mrs. Keating says that as a young housewife in Oklahoma with a broken washing machine, her first instinct was to ''call the repairman.'' He came, he saw, and he replaced a 5-cent washer - for $5, including labor. ''That was the last time that happened,'' she declares.
Most repairs are just this simple, she believes - once they're located. And with the help of the repair manual, most consumers can become competent do-it-yourselfers, says the woman who teaches plumbing, plastering, electrical repairs, machine repairs, and other courses to groups ranging from the Washington Suburban Sanitary Commission to the Congressional Wives Club, all in the Washington, D.C., area.
With the economy as it is, it is not too surprising that Mrs. Keating's classes fill up quickly. But with congressmen's wives? ''Helen Jackson (wife of Sen. Henry Jackson (D) of Washington) told me that money may not be the most important savings in home repair,'' says the fix-it woman. ''It's time she's trying to save - the time it takes to take a lamp in to be fixed and be returned.''
Not all of Mrs. Keating's students - or readers - are women. Her editor at the ''Homeowner's How-To Magazine'' - the first of many to carry her columns - refers to her as a ''handyperson,'' and most of her male students at recreation centers and the commission treat her like the expert she is. ''Occasionally you'll get a man who just won't know what to make of me,'' she admits. ''I had one student show up the first day of class and say, 'Oh, I thought you would be a plumber,' '' she reports. ''So I asked him, 'What makes you think I'm not?' ''
She thinks women have an advantage over men when it comes to repairs: ''Boys are expected to know all this stuff, and they don't dare admit it when they don't know. Women don't have to cope with (that expectation).''
Still, she never expected herself to be incompetent around machinery, saying that with her father's work, ''it was always there. I can't remember a time in my childhood when we called a repairman, but I can remember being allowed to accompany my father to Philadelphia to fix my grandmother's oil burner.''
She also learned by observing when her family bought an ''old bomb of a house'' in the suburbs of Washington, D.C., when she was a teen-ager - a 19 th-century beauty that was once a dairy. Today she and her husband live in that house and continue to repair it, room by room.
The repairs have to be squeezed in between classes (''I'm doing 30 right now for the commission''), weekly columns, and school. ''My father wasn't a women's-libber - he thought the only reason a girl should go to college was to catch a man,'' she says with an ironic grin. Now, with the children raised, she's a freshman at the University of Maryland. What's she studying? ''Electronics,'' she says with a smile. ''All this theory is starting to make sense,'' says the learn-by-doing expert.
Here are a few of her tips:
* Get the repair manuals for your appliances from the manufacturers, ''if you can talk them out of it. General Electric makes the best ones; they list the usual problems and their possible causes, tell you step by step how to fix them, and evaluate how difficult the repair will be.''
* Before calling a repairman, run these quick checks:
1. Is it plugged in?
2. Is the appliance plugged into a live receptacle? Try plugging a lamp into the socket, to see if it works.
3. Are all the controls set properly?
4. Are the water supply hoses kinked?
5. Has the light bulb burned out (a common problem with refrigerators)?
6. Has the ''emergency switch'' been accidentally turned off?
7. Is the vent duct open? Birds love to set up housekeeping in vents.
8. Is the thermostat receiving false signals from lamps, TVs, or sun?
9. Is the pilot lighted?
* Keep drains open by regularly treating with the following: Dissolve 1/2 cup washing soda in 1/4 cup warm water. Run hottest water down the drain for a few minutes, then pour down solution, completely dissolved washing soda. While the drain is still warm, flush the solution down with hot water.
* Use liberal amounts of cold water with the garbage disposal. Always run the garbage disposal before using your dishwasher.
* To remove water stains from bathroom fixtures, sprinkle cream of tartar over the stain and cover with an absorbent cloth. Saturate the cloth with peroxide. Allow it to sit until the stain fades, keeping the cloth damp.
* Keep all seams around tubs, showers, and sinks caulked. When caulking a tub seam, fill the tub with water so the weight will open the seams as much as possible.
* A good book for appliance repair is ''Popular Mechanics Home Repair Manual'' (the Hearst Company).
* If you have problems with a General Electric appliance, call the GE Answer Center for tips on how to repair it: 800-626-2000.
* If you have a plumbing repair problem, the Genova Plumbing Company has a hot line to call at 800-521-7488 (in Michigan, call 800-572-5398).
* For more tips, send $1 and a self-addressed, stamped envelope to Kay Keating, Box 30246G, Bethesda, Md. 20814.