RAINSTORMS, heatwaves, winds, air pollution, sun -- it's a wonder that lawn funiture survivors at all.

Lawn furniture manufacturers from Brown and Jordan to Molla to Sears agree on one major point -- keep it clean. Cleaning methods differ depending, on whether you have aluminum wrought iron or redwood furniture.

Proper care for the metal variety is simple. Arnold Schutzman, president of Stylume, a division of Brown and Jordan furniture, suggest washing the vinyl webbed seating with a mild soap: "We like to tell our customers, 'Whatever you use on your face.'" A mild soap is important because a strong detergent dries out vinyl's oil base, eventually causing it to crack. Schutzman adds, "If you do not clean your furniture often enough, dirt will get embedded in the vinyl and discolor it. Besides being unsightly, this also could cause the vinyl to crack."

For canvas seats, wash with a stronger detergent, rinse and dry. Some canvas seats have a water-repellent finish. After cleaning you might want to apply some Scotch Guard or Zepel, made Dupont -- two water repellents recommended by David O'Hearne of W. & J. Sloane.

Wes Gardner of Brown and Jordan points out that with pollution levels so high these days, it's a good idea to hose down and scrub your furniture every three weeks or so, depending on their use. "Don't let it go," Gardner warns, "or the hydrocarbons, given off by cars, will adhere to the vinyl webbing and you'll need a solvent to get them out."

Otto Molla, president of Molla Furniture, recommends cleaning their aluminum and vinyl lawn furniture with Fantastik a plain mild soap or with Dawn solution. Then go over the piece with a brush to get at any deep-down dirt. All of Molla's summer furniture cushions are "weathered" -- that is, they are designed to stay out in the rain. The filling is Dacron and Polyfoam, covered with vinyl and a die-fast cotton material. Not all outdoor cushions are rainhardy -- check the tags on the cushions now before the summer's first rainstorm.

Marie Schirmer, manager of Casual Gallery in Annandale, suggests applying a coating of automobile paste wax to the aluminum or wrought-iron frame each year to prevent it from getting scratched. Most aluminum frames are painted with a metal finish, while wrought-iron has an enamel finish. "And remember," she says, "suntan lotion and body oils are the two most damaging items where summer furniture is concerned. Suggest putting down a towel first. And if any lotion gets on the frame or seating wipe it off right away . . . If it builds up, it will ruin your furniture more than any kind of weather."

Sometimes the vinyl webbing or strapping dries out and shreds. Brown and Jordan will repaint and re-lace their furniture for a fee, if you send the piece(s) back to their factories in California or Arkansas. The cost is 60 percent of the new furniture's price, plus shipping. (All parts of Brown and Jordan's furniture are produced by hand labor, which is why the cost is so high.)

For a less elaborate re-webbing there are webbing kits sold at area hardware stores and Dart drugstores. All you need is the appropriate material, scissors and a screwdriver. Cut the material (usually vinyl-coated woven polyester mesh) into the size you want it. Then just screw it in. To keep the webbing clean, scrub with a mild detergent, rinse and dry.

Touch-up kits to repair chipped paint caused by oxidation also are available at local hardware stores, furniture stores or from the manufacturer.

To remove rust, W. & J. Sloane's O'Hearne says, "Brush the rust away with a steel brush and then repaint with enamel paint." A salesperson at Winslow Paints suggests using a rust remover, such as Naval Jelly, and then painting with a rust-resistant paint such as Derusto or Benjamin Moore's Retardo, neither of which need a primer; others say to apply a rust resister, like Rustoleum, and then apply a coat of paint, usually enamel. But it's better to avoid rust by keeping your summer furniture out of the rain.

Redwood furniture requires slightly different care. It contracts and expands with the weather. Redwood has the highest known resistance to termites. A spokesman for Sears Roebuck suggests re-applying a coat of redwood finish or stain on your furniture pieces each year to keep them glossy. Store them inside during the winter. For shorter periods of time use plastic covers -- this extends the life of the wood. Try to keep the funiture in a dry area or under a roof, where it won't soak up moisture. If redwood stands on newly poured concrete, cement or any other porous material, make sure the surface is completly dry. If not and it rains, the redwood may stain the surface. This stain can be removed with any household bleach.

Sears also suggests that when you buy a new piece of redwood furniture you rinse it off on the lawn first -- like washing a new pair of blue jeans -- to avoid having the color run on the patio. w CAPTION: Picture 1, Pine lawn furniture with a driftwood finish is protected by a 102-inch umbrella ($250): bench is $155; table, $165; chair, $120; at Lord & Taylor.; Picture 2, The pseudo Mies van der Rohe Barcelona chair stands up as patio funiture with solid aluminum frames. Chairs $315; ottman, $155; at W. & J. Sloane.