It's that terrible time of year when the stores are filled with beautiful fall clothes, at prices even more astronomical than the year before. You look at a dirndl skirt - one seam with a simple waistband - for $90. You swear to yourself, then and ther, that this is the year you learn to sew.

There have never been more reasons for taking a sewing class: You can get exactly what you want - fabric and style, the knowledge that it will fit in the right places, that you don't have to fight the crowds in the stores and, that you can save up to 50 per cent in price. Plus it can be fun.

Why don't more people sew? Maybe they're afraid to fail. Nobody wants to spend hours making a Vogue Yves Saint Laurent creation, only to loss it, red-faced, into the attic when it comes out all wrong.

So why not take a course - either a beginners' series, where you get all the basics and end up with several finished garments to show for it, or on a higherr level, to brush up on things you forgot from your home economics days, and learn some new techniques. There also are some interesting courses being offered in specialized areas like quilting , English smocking or making your own silk flowers.

Now is the time to take a sewing class, so next year at this time you won't be kicking yourself for letting it go another year. Below is a listing of some of the area's sewing classes. General Sewing Classes

Washington Fashion Academy, Silver Spring; 384-6924. Courses in dressmaking, patternmaking, menswear design and tailoring. Fee: $10 per two-hour class.

Y.W.C.A.of D.C.; 638-2100, Ext. 29. Workshop method classes for all levels. Offered every eight weeks. Fee: $32 for eight classes.

Ardis School of the Arts, Washington, D.C.; 234-6537. Eight-week courses in all levels of sewing, shirt-making , professional finishing (also extensive design programs, millinery and alterations). Fee: eight-week program and registration, $30.

Brother Sewing Machine of Washington, Washington, D.C.; 686-9500. Three levels of classes from making skirts to coats. Fee: $30 for six 2 1/2-hour classes.

Ritchey's Fabrics, Oxon Hill; 630-9700. Instruction in beginning sewing, knits, trousers and special teen courses. Fee: $15-$20 depending on the course.

Sadtler's Sew-Vac Center, Laurel; 498-2178. Basic sewing, fitting and dressmaking, men's jackets and machine-embroidery classes. Fees: $15-$20.

Designer's Fabric, Hendron, Va.; 437-9885. Short classes in basic methods, children's wear, fall T-shirts, machine embroidery. Fees: $3.50-$10.

Dannemann's Arlington; 524-8811. Basic sewing, dressmaking tailoring and pants tailoring. Fee: $12-$24.

Singer Sewing Center, Falls Church; 533-3121. Various level classes in dressmaking, teen sewing and knit sewing. Fee: $17.50-$29.50.

Sewing Machine Specialist, Vienna. Eight-lesson series in basic stretch sewing, tailoring, men's jacket. One-lesson seminars on lingerie, rugby shirts. Fees vary.

B.J.'s Dressmaker, Silver Spring; 871-6823. Individual or group lessons for all levels. You will complete at least one garment in the eight week-course. Fee: eight two-hour lessons, $40.

Judy Alderton, Montgomery County; 774-7653. Instruction in basic dressmaking, knit tailoring ultrasuede and teen classes. Fee: $16 for eight two-hour lessons.

Betty Stinnette, Takoma Park; Lessons in Bishop method sewing, lingerie, knits, rainwear. Fee: $20 for six lessons, two hours each.

Northern Virginia Community College, Loudon; 323-4555. Tailoring for men, classes in jackets and trousers. Fee: jacket class, eight lessons for $20; trousers class, four lessons for $12.50.

Toast and Strawberries, Washington, D.C.; 234-2424. A one-day workshop on Sept. 22 for people who sew and want advice from professionals on problems they are having. Fee: $12.50 for three-hour session.

Montgomery Ward. Most area stores offer basic and advanced courses in sewing and most fees are eight lessons for $25.

Sears. Many Sears stores offer basic and intermediate classes and several other sewing courses. The basic fee is $30 for eight 2 1/2-hour classes. Special Courses in Sewing with Knits.

Fashion Knit Fabrics, Alexandria; 360-5260. All levels of knit sewing classes, and also lingerie, children's and men's wear. Fee: Basic knit classes are six lessons for $18.

Sew Happy Sewing Center, Fredericksburg Va; 898-4547. Three levels of knit sewing and a menswear courses. Fee $19 for eight lessons.

Labett's Fabrics and Studio, Ltd., Beltsville; 937-4454. Classes in everything from basic knits to gauchos and sweaters. Fee: eight lessons of basic knit sewing, $20.

The Sewing Circle, Vienna; 938-3700. Instruction in basic knits, advance strech sewing and men's tailoring on knit fabrics. Fee: $19-$34.95 for series of seven or eight lessons.

Stretch and Sew, Falls Church; 533-3533. Basic knit sewing classes for eight weeks, two hours each, $20. Also a four-week children's wear course, $15.

Stretch and Sew, Springfield; 451-0155. Offers the basic as well as many specialty classes which meet for three lessons and cost $10. Including "Beautiful Blouses," the "Diane V Look" and "Creative Children's Wear."

Stretch and Sew, Vienna; 938-4741. Eight two-hour lessons in knit sewing for $25.

Kaytri McCowen, Cheverly; 772-6176. Techniques of sewing on knits, including polo shirts, slacks and cardigan. Fee: six two-hour sessions for $18.

Ms. Chan, Burke, Va.; 250-7762. Working with knits and ultrasuede. Maximum four persons per class. Fee: $35 for six two-hour lessons. Other Related Clases.

Eleanor Sienkiewicz, Washington, D.C.; 244-0781. Quiting for beginners and intermediates, from wall hanging to quilts. Six classes for $25.

Gingham Goose, Potomac; 299-1130. Introduction to quilting. Six two-hour classes for $36.

Terry Collins, Columbia; 730-4505. Classes in English smocking and how to alter patterns to include smocking. Four two-hour classes $20.

Long Reach Community Assn., Columbia; 730-8311. Courses in sewing bedspreads, curtains and drapes, pillows and quilting. Fee: $5 to $15.

Fashion Knit Fabrics, Alexandria; 360-5260. A two-lesson course in making silk flowers. Fee: $10.