A few weeks ago, I forever split the critical seam of my dearly beloved old blue jeans.

After a curse and a sigh, I had to admit it was probably time. So I zoomed off to the local jeanatorium for a replacement. In a moment of lunancy, I paid $21 for a simple new pair. And I threw what was left of the old ones deep into the rag heap.

It is this kind of transaction, and waste, that sends Ann Dickerson into a tizzy. She, however, does more than complain. For five years, she has run a boutique in Northeast Washington where the only things for sale are retreads.

The place is called Second Time Around. Its retreads are not just repair jobs; they are recombinations of very unlikely materials into rather startling new garments. When you have seen the lining of a discarded mattress turned into a spanking new caftan, you will never again think about fashion in the same way.

The same can safely be said of 81 impatients at D.C. General Hospital's Area C Mental Health Center. The Second TIme Around traveling troupe turned up here one day last week for a fashion show. After 45 minutes of viewing old ties rewoven into skirts and curtains redesigned into kimonos, the patients were clapping for more.

"I think it's wonderful," said one patient. "It makes me think I'm young again."

The 15 designers responsible for the show didn't have to pretend. All are 23 or younger, all attend high schools and colleges in the area, and all have fashion careers on the brain. In addition, each spends at least one day a week helping to run the home-base boutique at 518 Rhode Island Ave . NE.

But if the young folk are the arms and legs, Ann Dickerson is the heart and lungs.

She began Second Time Around wtih $200 and so much old material as she was able to beg. Now, "we aren't putting Garfinckel's out of business," she says, "but if you're one of those women who say, "I don't have anything to wear," maybe this is it."

Mrs Dickerson was herslf a model of stylish thrigt as she agreed patients arriving for the fashion show, She was wearing a khaki smock, much like the kind artists wear. "It's actually three of my husband's old Army Shirts," stitched together, she explained. "He doesn't know I took them yet."

Production cost: zero. Price: a relatively modest $20.

Second TIme Around goods are not just recombinations. Many of its designers simply retailer old dresses, many with big-league labels. These oldies-but-goodies drew just as large a response from the fashion show audience as the more bizarre modern stuff.

Part of the reason was the narrator's patter of An Dickerson. "Remember when taffeta was terrific?" she asked the patients. The older ladies grinned and nodded. "Mama had one just like this; Grandma had one, too . . . We always forget that what is old to us is new to someone else."

The Second Time Around secret, if it has one, is "cheating," Mrs. Dickerson admits. She means it in the sense of scrimping and not being afraid to break established design rules. "I tell my girls, there's nothing wrong with cheating if you do it right," she said.

But it's not just girls.

Mrs. Dickerson's son, Julian, 17, a student at Archbishop Carroll High School, stole the D.C. General show when he strutted out in the red flannel blazer and black bowler hat he designed for Valentine's Day. And back at the shop, many of the clothes are for men.

Students get 70 per cent of whatever their creaions sell for. The rest goes toward fashion shows and toward upkeep of the shop, which is located in an old row house a few steps from where the subway ends.

Prices range from $10 for a pantsuit to $100 for a mink coat. Mink coat? Well, it used to be an olive drab Army blanket before Second Time Around joined it with a few old minks.

"Each kid is considered not an employee but an owner," said Ann Dickerson. "This gives a young lady a real job experience. We teach them that each peron coming in that door is colored green. We don't want what you find everywhere else, somebody chewing gum and saying, "Ya want some-thin?"

At the fashion show, even though nothing was for sale, everybody seemed to want everything.

As each of the five models passed down one else of the psychiatric auditorium and back up the other, hands would reach out to feel the fabrics. "It's like nothing else we ever have here," said Isabell Smith, director of the mental health center's volunteer programs. "It's very therapeutic for everyone.

"It does give me satisfaction to come here," said Mrs. Dickerson. "Maybe we make them a little more aware of the things they throw . . . People like this need to see that there are real things in the real world."

For 18 of her 44 years, Ann Dickerson's world was her six children. "I was a housewife, period," she said. She began Second Time Around "because all my friends were saying 'You can't do anything else.'" The place has only broken even over the years, but that is more than one can say about some of Georgetown's neon trend dens.

"No sewing school in the city is teaching this kind of sewing," Mrs. Dickerson told the D.C. General audience, as one of her models, James Monroe, sashayed by. He was wearing what used to be the top half of a pair of military long johns. Now, it was sweater, with a spangled heart appliqued to the center. The applause was far more than polite.

The entire Second Time Around crew feels it is producing a style that is on the come."First we had the dirty jean generation, then the clean jean generation," Mrs. Dickerson said. "I think we're just in time for the dress generation."

Withthat, she throws a shawl over her shoulders. It used to be her grandmother's Saturday night satin dress. But there is not a whit of guilt or sentimentality in her voice. "You have to be creative and imaginative," says Mrs. Dickerson with a shrug. "Just give us the garbage of the world.