Don't be surprised if your winter skirts grew over the summer.

Maybe it was the new mothballs, who knows? But after trying on your skirts this autumn, they may seem longer than ever. Strange, you say to yourself, last year this skirt looked smart; it was right on the money. Now you want more skin where there's skirt.

Think twice before sending these skirts to the back of the closet, to a kind of wardrobe gulag. One or two of them may be perfect candidates for a little surgery. A skillful seamstress or dressmaker may be able to rescue a couple of old skirts, while saving you some money, too.

Requests for alterations already have increased since shorter hems have been making headlines. Roscoe Wright, of Paul Rosc'E, says he has started shortening hems from "just below the knee to just above."

But this may be only the calm before the storm. Genie Welch, at Frankie Welch of Virginia, an Old Town boutique that takes in outside alteration work, says she hasn't seen much demand for shorter hems yet. "It will happen though," Welch predicts, "once the customer sees the shorter skirts on the store racks and tries them on. Then they'll bring their old skirts in," Welch says. "There will be a huge rush in late September."

Unalterable Alterations Remember, some changes are irreversible. While things easily can be taken in or shortened, there may be no going back. A deep hem, however, is not the answer to indecision. Home-sewers might leave a large and bulky hem allowance in case they have a change of heart and want to go longer later, but most professionals don't recommend huge seam allowances -- not even for growing children. It just looks lousy.

Also, not all styles lend themselves to change. A knife-pleated wool skirt may not look good cut to mid-thigh. Any full skirts should be shortened with great consideration of the overall design and proportions. Says dressmaker Jackie Tyree at Sew Divine on Capitol Hill: "I never refuse to shorten a hem, but I will voice my opinion. I look at the figure and at how the skirt is made. Very full skirts and pleated skirts should be kept long."

Seriously consider having a straight skirt tapered as well as shortened. The narrowness of the new short skirts is what separates them from the minis of old.

Costs Whatever the cost of alteration, it's usually cheaper than buying a new skirt.

In general, most alterations shops won't give estimates over the phone. Every skirt is different, they say, and every little bit of detail will increase the price of the work. The simplest straight hem -- no lining or pleats -- may be $7.50-$10. A fully pleated skirt may cost $25-$50, since each pleat needs to be repressed. Skirts with a border printed into the fabric may have to be shortened at the waist and can cost considerably more.

Hemming knits can cost extra, and should be altered with great care. Ask the dressmaker or alterations shop if they can handle knits.

Hand-finishing costs more, as does anything lined. Tapering may cost a few dollars extra, but may do wonders for updating a straight skirt.

How High? The length should, above all, become the wearer. No one will give you credit for being fashionable if you look awful.

If you are not sure yourself, ask a friend whose opinion you value to come to the fitting, or ask the dressmaker to be honest with you. Don't be afraid to spend some time talking about what you want done. If it is a very complicated alteration, ask for another fitting before the final hem. Don't pick the item up while you are in a rush. Plan to try it on again before leaving. A good seamstress will insist on this.

The fit is most important. Patiently wait for the dress to be pinned in place and study the results carefully in the mirror. Most seamstresses like to place their own pin, so it's better not to bring something in already pinned unless it's a big emergency. "I don't like to work with someone else's pin," says Tyree. "The pinning is so important." If you are in a rush and don't have the time for a fitting, be aware that you are responsible for the accuracy of the hem measurements.

Where to Go Emily Cohen at G Street Fabric in Rockville suggests finding an alterations person convenient to you. Unless he or she makes house calls or office calls, you might find yourself traveling back and forth a few times for fittings. If you don't find a seamstress nearby, you might check the bulletin boards of supermarkets and libraries in your area. Many times at-home dressmakers and tailors advertise locally, in a small way.

Unless recommended to you, ask an at-home seamstress for the names of a few satisfied customers to call for references. At-home dressmakers can be less expensive and as skillful as one operating from a shop, but there is little recourse in case of dress disaster.

Although prices may not be given over the phone for a specific garment, you should be able to determine whether a seamstress' work is within your price range. "Prices vary a great deal," says Cohen. "Some just do alterations and some consider themselves dress designers and may charge more."

Area dressmakers and seamstresses specializing in alterations include:

District of Columbia Ardis Designing Studio, 1728 Connecticut Ave. NW, 234-6537. Open Monday-Friday, noon to 6 p.m., sometimes later by appointment. Hems shortened for $12-$50.

Cody Couture, 3062 M St. NW, 342-9015. Open Monday-Saturday, 10 a.m.-6 p.m. By appointment only. Alterations and dressmaking. Hems shortened for $10-$15. Takes about a week, although rush jobs are done at extra expense.

Im's Boutique, 2023 1/2 I St. NW, 331-8595. Open Monday-Friday, 10 a.m.-6 p.m.; Saturday, 10 a.m.-3 p.m. Dressmaking as well as alterations. Hems shortened in 5-7 days. $5-$20.

Julia Elena, 2737 Devonshire Place NW, 745-0037. By appointment only, Tuesday-Friday, 10 a.m.-6 p.m.; Saturday, 9 a.m.-2 p.m. Designing and alterations. Hems shortened for $12.50 and up, $80 to shorten a wedding dress.

MacDee Quality Cleaners, 1639 L St. NW, 296-6100. The seamstress, Sue Techanpanit, comes in Monday-Friday, from 1-7 p.m. Often she can do alterations the same day or the next. Hems shortened for $12 and up.

Margaret Menkart, Sewing Studio, 2614 P St. NW, 338-7450. By appointment only. Tuesday-Friday, 9 a.m.-6 p.m.; Saturday, 9 a.m.-5 p.m. Dressmaking as well as alterations.

Melvin's Custom Tailoring, 526 13th St. NW, 737-2100. Monday-Friday, 7:30 a.m.-6:30 p.m; Saturday, 9 a.m.-3 p.m. Tailoring and alterations. Hems shortened for $11-$16. Takes five days.

Nellie's Dressmaking Shop, 4211 9th St. NW, 882-8619. Monday-Friday, 9:15 a.m.-4:30 p.m. Hems shortened for $8 and up.

Pattraporn, 4200 Wisconsin Ave. NW, 966-6195. Monday-Friday, 11 a.m.-6 p.m.; Saturday, 11 a.m.-5 p.m. Dressmaking and alterations. Hems shortened for $12. and up.

Paul Rosc'E, 32 Rhode Island Ave. NW, 332-5673. Monday-Saturday, 10 a.m.-7 p.m. They make house calls. Dressmaking and alterations. A hem shortened for $10-$25. Takes one-two weeks.

Quality Fashion Dressmakers and Tailoring, 6400 Georgia Ave. NW, 882-3460. Monday-Saturday, 10 a.m.-7:30 p.m. Dressmaking, designing and alterations. Hems shortened for $6.50 and up.

Sew Divine, 901 East Capitol St. SE, 547-3355. Tuesday-Friday, 10 a.m.-6 p.m.; Saturday, noon-5 p.m. Other hours, by appointment. Dressmaking, designing and alterations. Hems shortened for $12 to $48.

Toast & Strawberries, 2009 R St. NW, 234-2424. Monday-Saturday, 10 a.m.-6 p.m.; Sunday, 1-6 p.m. Dresses copied, coats relined and alterations done. Shortening hems costs $9 to $20. By appointment. Estimates given over the phone. Takes 7-10 days.

Tyna's, 4627 41st St. NW, 363-2740. Monday-Friday, 10:30 a.m.-6:30 p.m.; Saturday, 10:30 a.m.-5:30 p.m. Tyna Schick does alterations as well as dressmaking. Hems shortened for $7.50-$20. Takes a week in general, but can be done in two days.

Maryland Aye, 7720 Wisconsin Ave., Bethesda, 986-8620. Tuesday-Saturday, 10 a.m.-4 p.m. Alterations and dressmaking. Skirts shortened in about a week. $10-50.

G Street Fabric Shop, 11854 Rockville Pike, has a list of area seamstresses and dressmakers.

Hecht's Department Stores. Monday-Saturday, 10 a.m.-6 p.m. The alterations department will take in outside work. Hems shortened for $8 and up for Hecht's purchases, $12 and up for outside work.

Parkway Dry Cleaners, 8402 Connecticut Ave., Chevy Chase. Seamstress available Monday-Friday, 7 a.m.-3:30 p.m. Fine hand-sewing and fitting. Hems shortened for $21 and up. Alterations take two to 10 days.

Virginia Frankie Welch of Virginia, 305 Cameron St., Alexandria, 549-0104. Monday-Friday, 10 a.m.-5:30 p.m. Hems shortened for $14 to $25. One to two weeks.

Hecht's Department Stores. Monday-Saturday, 10 a.m.-6 p.m. Hems shortened for $8 and up for Hecht's purchases, $12 and up for outside work.

Kwon Suk Im Fashion Designs, 1350 Beverly Rd., McLean, 827-0700. Monday-Saturday, 10 a.m.-6:30 p.m. Dressmaking as well as alterations. Hems shortened for $10-16.

Maria M. Snyder, Alexandria, 671-2071 between 7 p.m. and 3 a.m. to reach Snyder, who spends her day making alterations house calls in Washington and Virginia. She picks up and delivers garments in a day or two. Hems shortened from $8 and up.

Soo Young Lim Fashions, 804 W. Broad St., Falls Church, 532-3325. Monday-Friday, 9:30 a.m.-5:30 p.m.; Saturday, 10 a.m.-2 p.m. Dressmaking and alterations. Hems shortened for $10 to $18.

Vanessa's, 201 No. Fairfax St., Alexandria, 548-6623. Tuesday-Friday, 10 a.m.-4:40 p.m.; Saturday, 10 a.m.-4 p.m. Restyling and alterations only. Hems shortened for $10 to $25. Takes a week, but can do it overnight at extra cost.