One problem that crops up persistently at this time on both the outside and inside of many homes is mildew or mold -- a creeping grayish or blackish discoloration often mistaken for dirt when it appears on white or light-colored surfaces. On dark leather or clothing it often appears as a whitish, powdery-looking stain.

This type of mildew is actually a mold or fungus that is almost always present in the air. It spreads by means of spores that are often airborne, althought, they can be spread in many other ways. The mold starts to grow whenever the spores settle on a surface where there is an ample supply of "food" available, and where conditions are right for them to flourish.

For food they will attack almost anything that contains some organic material -- fabrics, leather, wood, paper and many types of paint. To live they need moisture, a reasonable amont of warmth and lack of sunlight and ventilation.

Inside the house, mildew is most often found in bathrooms and laundry rooms where ventilation is not adequate to dispel moisture and dampness, as well as in basements and closets where closely packed items are stored and where ventilation is almost non-existent at times.

Around the outside of the house, mildew is found on painted siding or trim that is heavilly shaded most of the day, particularly during sustained periods of dampness and/or high humidity. Mildew usually appears in the spring when dew forms on shaded area, and when surfaces remain damp for many hours.

As the mold thrives and spreads, it eats its way into and eventually destroys the surface on which it is growing. It discolors and rots fabric, leather, paper and many plastics, and virtually destroys paint if not killed.

In addition, mildew often leaves a musty odor that is difficult to get rid of in indoor spaces.

Although the mildew that forms on leather, fabric and paper is easy to recognize, that which forms on painted surfaces, especially around the outside of the house, is often mistaken for dirt. Homeowners wash it off with detergent, and if most of the discoloration disappears, they assume that there is no problem and put on another coat of paint.

More often than not, the mildew will soon grow back -- only this time it will be more intense and more widespread than it was before because the fresh coat of paint supplies it with additional food.

One sure way to test for mildew on a painted surface is to apply a few drops of fresh liquid laundry bleach to the suspected area, without scrubbing. If it is mildew, the dark stain will disappear within a minute or two. If it is dirt, it my bet slightly lighter, but it will slightly lighter, but it will not disappear completely -- at least without considerable scrubbing. One caution: The bleach must be fresh for this test; bleach that has been in an open bottle for six months may no longer be effective.

The most effective way to remove mildrew from a painted surface is to either spray with a mildewcide sold for this purpose in many paint and hardware stores, or scrub with a solution of one part liquid laundry bleach and three parts water. To a bucketfull of this mixture, add about a cupful of powdered detergent.

Scrub this on over the mildewed areas, then allow the surface to dry (wear rubber gloves to protect your hands). Flush with plenty of clean water, using a hose, if practical. On the inside, use a sponge and a bucket of water to rinse the surface, but change the water frequently.

This treatment should kill the mildew spores remaining on the surface, but this, of course, is no guarantee that they will not return. If possible, try to provide more ventilation to the area, and if it is on the outside, trim away shade trees or shrubs that keep sunlight out. On the inside, arrange for more ventilation in any affected area (in kitchens and bathrooms an exhaust fan may be needed), or consider getting a dehumidifier.

Bear in mind that if mildew shows up on painted or papered walls, it may have penetrated to the paint on other surfacing material underneath (the paper facing on the gypsum board, for example), so there is a further possibility of its return.

After the mildew has been killed and the surface cleaned as described, it is advisable to repaint as soon as possible with mildew-resistant paint, or paint to which additional mildewcide has been added. Some companies formulate paints specifically for this purpose, but if this is not available locally, there are mildewcide additives that can be mixed with the paint just before using it; (one band available through paint stores is X-14 Mildewcide Paint Additive, made by White Laboratories, P.O. Box 15335, Orlando, Fla. 32858).

As a rule, hard, glossy finishes are less likely to mildew than softer finishes, and all paints are most likely to be attacked by mold spores while they are still soft. Thus, if paint is applied when the atmosphere is too cold to allow it to dry promptly, it is more likely to provide a home for mold spores while it remains soft -- even though it eventually dries hard.

The same is ture for indoor paints -- harder finishes are more resistant to mildew than softer finishes.

Preventing mildew in other parts of the house, or on various items inside the house, is usually a matter of trying to eliminate the conditions that contribute to the growth of mold. Where mildew growth could be a problem, take all steps necessary to eliminate dampness.

Sometimes the addition of a little extra heat in a closed-off area is all that is needed (for example, a light bulb left burning in a closet may be enough to keep the contents dry).

In basements or laundry rooms, make sure the dryer is vented directly to the outside, and add an exhaust fan if the room usually gets humid or steamy when in use. In closed basements, a dehumidifier (chemical or electric) can be used to absorb moisture, and in closets, bags of moisture-absorbing chemicals can be hung to remove dampness.

Another point to remember when combating mildew is that clothing, furniture and other objects should be cleaned before being stored -- dirt and soil provide excellent breeding grounds for mildew spores. So does a fine layer of grease or soil on walls, ceilings or furniture.

When mildew is discovered on clothing or furniture, try to take the objects outside before brushing or shaking so the spores won't get scattered around on the inside. Sunlight is excellent for destroying spores and for getting rid of musty odors.

Mildew spots that won't brush off can sometimes be removed with a solution of denatured alcohol and water (half and half), or if safe for the fabric, try lemon juice and salt. Clean by washing or dry cleaning (as appropriate) if this is practical. Otherwise, hang the garment out in the fresh air to dry.

Household fungicide or disinfectant sprays are good for protecting leather and upholstered furniture or mattresses, as well as for removing and killing mildew. Sprinkling with talcum powder or cornstarch will help dry books and papers.