A day in the garment district? You have to be joking. We are talking about 12 blocks of 7th Avenue with half a dozen side streets, and you walk into a 20-story building and look at the lobby directory and every single entry is a dress company. Four columns of dress companies. One day?

It's not even 9 o'clock, and already they're drifting into Dubrow's Cafeteria for the first coffee: plump, intent men with their hats on and gray-wigged women in girdles. Hardly anyone seems to be over 5 feet tall.

On the street the young executives stride past, anyway they're dressed like young executives: wide lapels, pinched waists, shoulders like epaulettes, everything pressed that very morning and the shoes gleaming plastic. What they are is salesmen, and the shoes are very important. (Their fathers shined their shoes every single day, on a newspaper laid over the toilet seat, because shined shoes said prosperous, shined shoes said I am somebody.)

Look out for that cart. It's the size of a sawed-off piano and it has a rack on top of it made out of old iron pipe and it's got about a hundred of the same white dress on hangers packed down the length of it. A kid in sneakers (they all wear sneakers) is pushing this battered vessel along the street on its rollerskate wheels that rattle like a bunch of hexagon nuts being swizzled in a garbage can.

These carts are the trademark of 7th Avenue. All day long they trundle here and there, loaded or empty, braving the traffic and treated by the New York cabbies with no less or more respect than any other vehicle.

There is a sidewalk version: a suit-case on two little wheels being rolled along by a portly middle-aged man with a harried expression. In the garment district everybody who is not pushing or pulling is carrying something.

Shop windows: "Clearance Sale! SENSATIONAL: Aquascutum Raincoats $19!"

Another window contains nothing but three bushels of zippers and piled boxes of safety pins. Millions and millions of safety pins.

Beau Bakar is on the phone again.

"Four-fifty! He want $4.50! I told him 4 is all I can do. But what do you want? For 30,000 yards of velour - What? And he's talkin' August delivery. I said it's gotta be June or forget it ..."

Beau Baker is dressed like a young executive. He is a young executive. He didn't get that tan under a lamp. A medallion gleams in his open collar, a gold watch gleams in his open collar, a gold watch gleams on his wrist. He talks in numbers a lot, percentages. He runs Tracy Petites. His father is Jack Baker, who runs Sue Brett. Fashion houses.

"It's not all that a family business though," he says. "This business, it's the kind of business, it's like carrying a pail of water with 11 holes in it."

First, you decide on the fabrics for your next line. (The sofa in his office is pile 5 feet high with swatches bolts, and you can't even see the armchair.) You shop the market for new ones, guess which of last year's will come on stronger this year. Then you make up a group of dresses in each of these fabrics.

"In fashion house you do three, four, five different dresses, depending on how strong you feel about the new line. Use a variety of silhouettes, two-piece, one-piece, short sleeve, long sleeve. The designer makes 'em the way she feels they should be made, she's free to do what she wants, but you try to train a designer to your means. Five, 10 years ago you had to strip everything down, cut down on the buttons and trim and things, but today people want quality. Sometimes you even need to build a dress up."

The samples are constructed and priced - cost of fabric, stitching, labor, trim, purchasing - and the markup is added.

"A 30 percent markup is a lot, but over head can run you 15 to 20 percent, and with everything else, and the mistakes, you can wind up with a profit of 5 to 8 percent if you get stuck with too many piece goods. On the other hand, you can make a fortune very fast."

The line is shown to buyers and sold in quantity. Some stores order three or four numbers in one style. Mixed lots. The big department stores buy 18 to 24 versions of a style and will reorder ir they sell well. The grading and marking department lays out cardboard patterns for all sizes on a huge piece of paper 20 yards long, the marker. Squeezing in the maximum number of garment pieces, maybe 500, on a single marker is called making a tight markerM and it is a skill that pays off.

Leonard S. Bernstein tells about "shrinking the marker" in his book, "How's Business? Don't Ask!": Back in the scruffy past, a small-time garment manufacturer named Seymour once received a marker that had been ruined in the mail, squashed into one big ball. Not having time to send for another one, he smoothed it out as best he could and laid it on a stack of 300 layers of material.

Lo and behold, the marker was now only 19 yards long instead of 20. That meant Seymour could save 300 yards of material. Well, 1931 was a tough year in Allentown, Pa., so Seymour had his cutters use that shrunken marker, not only that but when the next order came in he took the new marker into his office and balled it up himself.

Now, people on 7th Avenue will tell you this is a myth, it never happened, and there's no one named Seymour in the garment industry. But why is it tha t with some houses you are a size 12 while with others you are a 14?

So here we are with a roomful of bundles: 500 left sleeves, 500 right sleeves, 500 collars, 500 left shoulder panels, 500 right shoulder panels and so on, each bundle held together with big rubber bands, and what do we do now? We send them out to contractors to be sewn up.

And at this point we become particularly aware of the garment workers union. There is a price for everything, and everything has its price. A long stitch costs so much, a short stitch so much, hems, button-holes ... every run of stitches on a garment has to be costed out. The union is a fact of life in the district. The only problem, Baker says, is that "70 percent of our competitors are producing in nonunion shops."

It takes two or three weeks for an order to be sewn up. Then the dresses start coming back, maybe 4,000 a day, to be shipped off to the department stores, specialty shops and boutiques.(But no discount houses, not for the likes of Tracy Petites.)

"You give yourself eight to 12 weeks to put out a line, from the idea to the store. But it can be done in three weeks if you're really excited about it. In 10 weeks you can produce about 100 styles. A good style will run maybe a year, possibly two. A bad dress will run a week."

In its heyday in the Beatle era, the great London boutique Biba used a computer to project sales. Owner Barbara Hulanicki, who in those days designed everything herself, said she could tell within two hours of a dress appearing on the floor almost exactly how many she would sell. Even without a computer, the saying goes, "If a dress is great, you would know about it the first day."

About those others: well, you mark them down. Sometimes you get back half your cost. But there's a market for everything, even damaged garments. Some women will buy a $40 dress that has a tiny hole in it and feel they're one-up on the world. There even used to be market for scraps of wool, cotton and synthetics.

"People will always buy fashions," Baker says. "The customers don't know what they're looking for, but they have this uncanny way of walking into a store in Washington or Denver or Seattle or Philadelphia or Cincinnati, and they can see the same three styles, and one will sell and the other two just sit there. Nobody knows why. I can make a dress in six colors and two will go crazy but the others are just wrong somehow."

On his desk: a color chart with small rectangles of fabric - mauve, rose,cinnamon, marine blue, gold, plum, taupe, lilac, peach, cedar brown.

"Anybody can produce a dress. There's always a lotta small people with low overhead. When something gets hot, nobody can produce it fast enough and the supply may not catch for months. In that time you'll get five, 10, 20 people making the same thing. The original will always sell the best, but 70 to 80 percent of the market is made of people who do nothing till they hear what dress is selling in the stores and then they copy it. It's the fabric that sells 'em. Fabric is the crucial thing, then color, then design. I can predict accurately for four to six weeks ahead, though the business can change drastically in that time. I can project a trend up to six months.

"But on the other hand if something really good comes along it can be too good and saturate the market, and you have no way of knowing when that's gonna happen. And then you can get some trend out of nowhere like'Annie Hall.' I don't know. The signs are always there; it's reading them that's hard."

Leonard S. Berstein insists that there exists on 7th Avenue a practice called "knocking off a style." This is when a manufacturer wants to save money so he fires his designer and goes out and buys some likely looking dresses at Saks and Macy's and copies them. THis can be strictly an emergency as when the designer has quit the day before and the new line is due today. Or it can be, unfortunately, a habit. Some garment firms are known as "known-off houses," and they are not highly esteemed by the others.

It is 5 o'clock and men are sitting around the office in their shirtsleeves watching a couple of colleagues struggling to zip a plastic cover over a rack of dresses on a cart.Finally they get it load. Shrug into their jackets. Shove the cart laboriously across the deep pile carpet toward the door.

It is 5 o'clock and the elevaots are jammed with women, all ages - cutters trimmers, sewers, pattern makers, designers. The sex roles seem unusually rigid in this business: When you speak of a designer you automatically say "she." The young ones are dress ed to beat the band.

It is 5 o'clock and the sidewalks and even the streets themselves are awash with people flooding toward the subway, and you still haven't found out why it's considered bad luck to sit on a cutting table, in fact you haven't even seen a cutting table yet.

One day? A year? You could spend your whole life on 7th Avenue ...