Wood is wonderful, but it does have some shortcomings; one of these is its vulnerability to rot, which can turn even the hardest oak into a crumbling, powdery mass.

But if you detect the rot before it goes too far you can halt the process and restore much of the wood's original strength.

The secret is a penetrating epoxy formula sold under trade names like Git Rot or Cure Rot, which go deep into the wood to seal it against moisture and bind its fibers back together.

Rot restorers aren't cheap, often costing more than $10 a pint, but when part of your home - usually an outside windowsill or threshold, or wooden gutter - is hit by rot, restorers are often the cheapest, easiest solution.

They are really intended for use on boats, so you can usually buy them at marine centers; you can also buy them mail order from outfits like Brookstone, 127 Vose Farm Rd., Peterborough, N.H. 03458.

To use one, make sure the wood you want to treat is dry and free of any paint or varnish that could interfere with penetration. Work only when the temperature is between 50 and 75 degress: The epoxy won't cure well at low temperatures, and may cure so fast it won't have time to soak in at higher temperatures.

Check the depth of the rot by probing with an icepick. If it's more than half an inch deep, drill a series of small holes into the area to be treated, to help the epoxy get deep into the rotted wood.

Then mix up the two-part epoxy according to label directions. Start at one end of the rot. Apply the epoxy by brush or by pouring, working continuously to the other end of the rot. A random pattern may trap air inside the rot, interfering with penetration.

Spread the restorer with a paint-brush, taking care to fill any holes you drilled. Don't brush the stuff out as you would paint. Keep the wood good and wet, and be sure to apply the restorer to every accessible surface of the rotted wood. End grain will soak up epoxy faster than other parts of the wood, so flood end grain heavily.

Let the epoxy cure for 24 hours. Then you can begin final finishing, if desired, treating the restored wood just as you would new wood. Sand it smooth. Fill any cracks or holes, including those you drilled to encourage penetration. Sand the putty smooth and paint if you like. Porch and deck paint will hold up well on a threshold, ordinary house trim paint will do the job on a windowsill.