One of the worst jobs any homeowner can face is stripping all the old paint off his house, right down to bare wood. It's dull, tedious, even dangerous, and it can take a long, long time. But if your old paint is blistered, cracked, alligatoring and peeling away, the job has to be done. A fresh coat of paint won't solve the problem.

One way out is to have the house stripped by a professional sandblaster. He and his crew come in with huge air compressors and a truckload of sand and literally blast the old paint right off your siding. In fact, the abrasive action of the sand will even remove a thin surface layer of wood. This can be a good thing, since it produces a clean fresh surface, but it can also have its drawbacks.

If you think sandblasting might be for you, here are some precautions to take in hiring a contractor:

Get bids from two or three sandblasters. A reputable contractor will come to your house, look it over carefully and give you a price for the job. Make sure you know what is and what is not covered in the work he will do. Will he strip windows and trim as well as siding? This kind of work usually can't be done by the blaster's gun. It requires hand work that can jack up the price.

Will the contractor clean up after himself, removing sand and debris from your gutters and from around the house? Get all these details down on paper before you pick your man.

A good contractor will also warn you if your house is not suitable for sandblasting. Certain types of siding will wear evenly under the action of the sand, but other types will be blasted into a wavy texture that corresponds with the grain of the wood. Most homeowners don't like that look and should stay away from sandblasting if they have certain types of siding.

What types of siding are those? Any with flat grain rather than edge grain. As a rule, shingles and good grades of lapped cedar siding will be edge grain. Cheap cedar siding and most types of pine siding will show a lot of flat grain. It's unfortunate that flat-grain siding doesn't respond well to sandblasting, because flat grain is especially poor at holding a coat of paint, and is therefore often in need of a good stripping.

Sandblasting requires a certain skill. A careless or inexperienced worker can literally blast a hole through your siding, so it's a good idea to ask any contractor you are considering to show you some of the other work he's done in the past. Have him show you a house or two with siding similar to the siding on your house. If possible, ask the owners of those homes for their feelings about the contractor and the job he did. Also check him out with the local Better Business Bureau and your bank. Sandblasting requires a lot of expensive equipment, so it's not a profession that lends itself to fly-by-night operators. Still, it's best to check your man out before hiring him.

Finally, once you pick your man, do not give him his full fee until the job is done to your satisfaction. Pay half at the start of the job and the other half at completion. Once a contractor has his money it can be very difficult to coax him into touching up those small details that often remain unfinished at the tail end of a job. CAPTION: Illustration, FLAT GRAIN, ABOVE, AND EDGE GRAIN.