IN THE days before air conditioning, Washingtonians marked the onslaught of the summer months by hanging sheer curtains instead of heavy ones; slipcovering the upholstered furniture; and laying sisal area rugs after calling Nazarian Brothers to pick up, clean and store thick wool rugs.

A number of rug cleaning companies are available in the Washington area. Some will clean the rugs at your home, while others only work at their plants.

You may want to clean your carpet yourself. Cleaning rugs -- not just vacuuming, but thorough cleaning -- is a tricky business. Colors, especially the often over-dyed threads in Navaho rugs, may bleed. Expensive and inexpensive dyes can bleed, as can natural and synthetic ones. How successful cleaning also depends on the tightness of the rug's weave.

Clarissa Palmai, conservator at the Textile Museum, says "The best advice I can give someone is to go to a reputable cleaners. Don't do it yourself unless you really know what you're doing. It's no big secret -- there's no specific recipe -- but sometimes people don't follow our advice exactly."

Mike Holtzhauer of Dyna-Brite agrees. "Do-it-yourself treatments can get good results, but a professional usually gets results every time," he warns.

The Textile Museum, which houses many fine tapestries and rugs from all over the world, does not recommend any particular rug cleaner to people who call. Says Palmai, "We get over 20 calls a day asking for names of good cleaners. We don't give out names because the one time we did something went wrong at the particular cleaners and rug owner wanted to sue the Museum!"

If you're determined to clean your rug yourself, test the colors carefully for bleeding. The Textile Museum offers demonstrations on rug washing. They suggest you test rug colors by applying a drop of water on a tiny portion of the rug and then pressing a tissue against it. If any color comes off on the tissue this means the colors will run. Palmai says you should also apply a drop of soapy water to the rug to test for the same thing. "Some dyes don't react when exposed to water, but do react to detergent," Palmai says.

Steam machines can be purchased or rented at High's for about $12. You pay $7 to $8 more for the proper chemicals. If you want to rent a shampooer at a local hardware store that will also cost you. All in all, the cost is not much cheaper than it would be to have the job professionally done.

In the rug washing demonstration at the Textile Museum you're shown how to immerse the entire rug into big washing pans of water or into a dry cleaning solution. How to hang the rug to dry is also demonstrated. Drying takes about 24 hours.

Peter Levonian, plant manager at Neshan Hintlian Rugs, 3323 Connecticut Ave. NW, says they clean oriental rugs at their plant, never at the customer's home. Hintlian picks up the rug and delivers it when done. Depending on the distance, they may charge extra. "We didn't used to, but with the price of gas, we were forced to," regrets Levonian.

"Before we do any cleaning," says Levonian, "we look for damages and test the dyes. If there are any tears or if the dyes run, we contact the customer. If they give us the go-ahead we clean the rug. When colors bleed we do our best, but don't guarantee anything."

First the oriental rug is beaten with a beating machine, which takes the dust out.The rug is run through the machine as many times as is needed to get it relatively dust-free.

Then the washing process begins. Hintlian uses a special shampoo detergent which they mix in a tank with water. The rug is then dampened with water and the shampoo mixture is applied to the rug with a vacuum-like machine. The rug is rinsed thoroughly and then put through a wringer machine. Once most of the moisture is wrung from the rug, the rugs are hung in a hot room. "In the summer," says Levonian, "we don't use heat, we just hang the rugs in the plant and put a fan in front of them. You have to be careful that the rug doesn't burn.

Hintlian charges 42 cents per square foot for rugs that are 9 by 12 feet and over. If the rugs are very heavy and hard to handle, the price goes up accordingly.

Nazarian Brothers, at 2323 Wisconsin Ave. NW, uses the same basic process. President Elsie Nazarian says their beating machines consist of leather straps that are operaed manually to dust-clean the rugs. They then place the rug on a concrete floor and apply high pressure cold water to the rug's surface and back. Then they pour a soapy solution onto the surface. It is brushed into the rug with a round circular movement. The rug is then turned over and the back is washed in similar fashion. Both sides are hosed down again and then wrung out.

"It's very important to wash the underside of the rug as well as its surface, the dirt is merely flushed down to the back of the rug."

After being wrung out, the rug is rolled out onto a long table. A rod is lowered from the ceiling of the plant and the rug is hung up with thin pins. The rug is then suspended from the 30-foot high ceiling until it dries. Hot air vents in the ceiling give off a warm and balmy air that is best suited to drying rugs.

Nazarian Bros. has a minimum fee of $60, and beyond that they charge 50 cents per square foot. If the customer delivers and picks up the carpet, the minimum charge is only $54.

Dyna-Brite Systems, 10705 Margate Rd., in Silver Spring, does all its work on location at the customer's home. President Mike Holtzhauer says they get the same results as they would if they worked in a plant.

At Dyna-Brite steam cleaning is used as opposed to shampooing. "The problem with plain shampooing," says Holtzhauer, "is that shampoos loosen the soil and drag it to the bottom, where it's out of sight. The idea behind the shampoo is that once the rug has dried, the customer can vacuum out the remaining dirt. Unfortunately most of the dirt stays in the rug.

"Leaving shampoo in the carpet is like not rinsing your hair after washing it or not putting your clothes through a rinse cycle. It causes whatever it is to soil faster," adds Holtzhauer.

With steam cleaning, Dyna-Brite may shampoo the rug first to loosen the soil, but then the soil is steamed out, meaning that hot water is flushed through the carpet. (This process has many names besides steam cleaning, such as stream cleaning, hot water extraction, jet extraction and deep soil extraction.)

"For awhile," says Holtzhauer, "the Better Business Bureau was against the use of the word 'steam' in advertising, since the process actually uses hot water and not steam. But since 1978, they've relaxed their regulations."

Ken Orr, vice president of the Industry Standards Division at the Council of Better Business says "Yes, at one time we were worried that the consumer was being misled by the word 'steam.' Steam is not used. Hot water is. If steam were used -- since it requires a temperature of 212 degrees or higher -- the consumer's carpet would be burned. But since 'steam' seemed to connote so many different definitions to different people, we finally rescinded our request."

In addition to the shampoo and hot water, Dyna-Brite also uses one of 35 different stain removers to help extract stains.

Louis E. Cimaglia, president of Metro Buff Away, who handles all of Woodward and Lothrop's residential on-location carpet cleaning, employs neither the shampoo nor the steaming methods, but instead uses something he calls "electro-static withdrawal." A fluid Cimaglia calls "Buff-Away" is applied to the carpet. It works by changing the polarity of the dirt to a like charge with that of the carpet. The soil is released and repelled from the rug. The dirt is held in suspension until a pad with unlike charges is rotated on the buffing machine beneath the rug, attracting the suspended dirt. The dirt remains on the pad until it is neutralized by a washing.

Cimaglia says he has the only patent on the electro-static withdrawal process in this area. The process was invented, he adds, by the Industrial Consulting Corp. in Philadelphia.

Cimaglia claims for his process:

The usual drying time of 8 to 48 hours for a rug is reduced to less than an hour.

No shrinkage or injury to the rug guaranteed.

The chemical in "Buff-Away" has a sanitizing effect; it will kill 99.9 percent of the bacteria in the carpet.

Virtually no residue is left in the carpet, including soap. (Cimaglia says that even hot water extraction doesn't rinse out all the soap.)

Buff-Away charges 21 cents per square foot.

For everyday care, carpets should be vacuumed regularly -- once a week is good, but as Mike Holtzhauer of Dyna-Brite Cleaning says "I don't do my own rugs that often."

When vacuuming, warns Elsie Nazarian, be careful of the fringes.

"Don't vacuum to the ends of the fringe, since they're easily caught or chewed up in a vacuum." After a rug has been cleaned, Nazarian recommends turning them so that the same side doesn't get all the traffic and wear down faster than the other side.

Nazarian also suggests dusting or vacuming the pads or rubberized facing beneath your rugs -- they don't need washing.

For spills Harold Keshishian of Mark Keshishian and Sons, Inc. suggests that you apply a mixture of detergent (like Tide) and water to the spill. Take a Turkish towel and using a rotary motion, work the solution slowly around, making larger and larger concentric circles.By working the stain out, no ring will be left, Keshishian says. (Keshishian handles mostly Oriental rugs and charges 60 cents per square foot for them. For domestic carpets, they charge 40 cents per square foot.)

How often should a carpet be washed? It depends on the owner. Twice a year perhaps, if you have a lot of kids, pets etc. or do a good deal of entertaining. And maybe every third year if your life style is less hectic.