A booming business. Tomorrow night, the skies of about 900 US cities will sizzle and smack with pyrotechnical wonders designed by the flamboyant Zambelli family

IN an old, one-room workshop with a crucifix over the open door, Joseph Zambelli wraps silvery aluminum and potassium perchlorate powders in bits of newspaper, tying them by holding one end of a string in his teeth. Beside him, Benny Siciliano loads cardboard cylinders with small black balls of chemicals that will explode into color and sound. The two men work entirely by hand, since machinery might cause a fatal spark. Shouting to each other occasionally in Italian - Mr. Zambelli has damaged his hearing in explosions over the years, and Mr. Siciliano prefers his mother tongue - they work according to formulas and procedures that have changed very little for centuries.

Tomorrow night, the fireworks they've assembled will be detonated from electronic firing boards, synchronized to music with computer-generated timing cues, and illuminated with lasers.

Such are the art and science of fireworks at Zambelli Internationale.

Once a moonlighting business run by Joe, his brothers George and Louis, and their father, Antonio, Zambelli Internationale Fireworks Manufacturing Company is now arguably the biggest fireworks manufacturing and display operation in the United States. Under the direction of George Zambelli, pyrotechnicians will supply three-quarters of a million shells of fireworks for displays in 900 cities this Independence Day.

For the Zambellis, there is no night quite like the Fourth.

Since Easter, the company's two manufacturing plants have been running seven days a week, 10 hours a day, preparing for the one night of the year when they will do about 75 percent of their annual business. For the last month a steady convoy of trucks has left the warehouses in New Castle, Pa., bound for cities as diverse as Las Vegas, Nev.; San Diego; Indianapolis; Miami; Philadelphia; Atlantic City, N.J.; and Tulsa, Okla.

Two weeks ago, at corporate headquarters in New Castle, company president George Zambelli - a.k.a. ``Mr. Fireworks,'' ``The Great Zambelli,'' and ``Boom Boom'' - was answering seven phones and hurling orders at his staff, which includes three of his daughters.

After seven years of coordinating work orders and truck deliveries, Annlyn Zambelli still approaches her father's office with caution. She takes a moment to chat on the phone with her sister, Marcy, manager of the Florida office, which provokes George's scowl. Danabeth Zambelli trips into the office with a bright smile. She's been working at the company full time since last December, helping with bookkeeping and learning the ropes. Now, at 23, she exercises a youngest child's privilege, joking with George, as seasoned men wince under his sharp commands.

Later, George is fuming over the mixture of business pressure and family dynamics. He has been a hardworking man all his life, used to 18-hour days. ``They were yakking away in there - c'mon, this is a place of work. I'm the boss, I'm the father; how am I going to entice someone else to move if they get away with it?'' He slumps in his chair, rumpled and irate. ``Now they're mad at me.''

Outside town, at the new plant on Nashua-Harbor Road, hands hired for the season bring the number of employees working in shipping and manufacturing to an amazingly scant 32. An additional 2,000 trained technicians will shoot the shows. In the warehouses, workers preassemble and number as much of the displays as possible before they're boxed. ``Florida, South Carolina, and Georgia are almost done,'' a worker calls out as his supervisor passes by. A line of yellow Hertz trucks waits to be loaded.

In the low concrete workshops scattered across the hillside, the calm, meticulous manufacturing process, every step performed by hand, resembles a scene from another age. Doors are propped open at both ends of each building to vent any explosion. No more than two or three workers together share space with boxes of black powder, brown paper, and shells.

As he has for 40 years, Louis Zambelli works at a wooden table, ``rolling bombs.'' Slapping wallpaper glue on a sheet of kraft paper, he wraps up a long fuse and a Green-Colored Peony from Japan.

Like most US fireworks artists, Zambelli choreographers use a combination of imported and domestic shells, with a worldwide choice of thousands. Louis and others add the outside fuse and lifting powder to both imported and Zambelli-made shells here at the new plant, where Louis, formerly vice-president of production, supervised for years.

Each shell and its manufacturer are known for certain effects. ``Nobody, but nobody, makes salutes the way we do,'' exults George, referring to the loud bangs that he considers quintessential fireworks. Another Zambelli specialty, says Louis, is ``flitter,'' a diamondlike twinkle of color made from 80 percent black powder. Zambelli shells with names like Stars and Shots, Whistles, and Eight-Break Spider Web With Report burst repeatedly into showers of sparkle and sound.

Names and images are important in this fiercely competitive industry, as is the appeal to the imagination. The temporal magic of the product itself is embodied in the flair of its producers. The top US companies, a handful of close-knit Italian-American families, speak of themselves as artists and regard one another with suspicion and pride. They are creative and business people, and consummate showmen.

``It's like being an actor, entertaining people; you like to see them entertained,'' says George. Handing out T-shirts and red pens, throwing his seemingly boundless energy into imitations of fireworks effects, he takes to the role like a circus promoter. Company slogans proclaim ``Zambelli Since Fireworks,'' and myths of old family secrets sparkle like flitter.

There is nothing bland about any Zambelli. With their frosted curls, heavy jewelry, and silver shoes, Annlyn and Danabeth are eye-catching; Marcy is a former Miss Pennsylvania.

But behind the promotional images is the story of a hardworking immigrant family determined to succeed. Antonio and Maria Zambelli came to the US in 1921, raising seven children during the Great Depression. A fireworker in Casserta, Italy, Antonio worked in the steel mills of New Castle until his oldest son, Joe, bought out a family-run fireworks shop on the outskirts of town.

After World War II Joe, Antonio, George, Louis, their brother Carmen, Louis's wife, Diane, and their sister Rita's husband, Sam Caimano, pitched in together making and shooting fireworks. George, with a degree in marketing from Duquesne University, became a tireless promoter. And the company took off. Ten years after the war, Louis recalls, it was one of the biggest in the country.

Danger stalked, as it does through the industry. In 1950 Caimano was killed in an explosion. Joe was injured building a display scaffold, when his hammer struck a spark from a nail. His wife, Mary, and Louis's wife, Diane, encouraged their children to go to college instead of entering the business. George's children work only in the office.

As experienced manufacturing workers grow older, George mutters with some seriousness that he's going to Italy to look for craftsmen. The handwork is a dying art in the US, he says: No matter how good the safety record these days, people just don't want to do it anymore.

But out at the old plant, Joe and Benny Siciliano walk outside their shop in the knee-high grass, carrying a little cardboard shell that they have taped together in lieu of Louis's finishing operation.

``I was crazy about this kind of work,'' says Joe, recalling the early days of the company. ``You gotta have twine, paper, powder - the only thing is, you got to know how much to put in. Red, green, blue, yellow, I can make any kind of fireworks you want.''

He sits heavily on a bench, while Siciliano carries the little shell out to a steel mortar in the grass and lights it. Whoosh, bang! and white streamers of smoke float out against the blue sky. The two men smile without comment.

Against the backdrop of the night, thousands of their shells of all sizes and colors will be launched in 20th-century splendor. This is young people's work, technological wizardry. From an electronic control panel with hundreds of buttons, color and sound are synchronized through the coordination of tapes, computers, and cables.

The crowds pause in anticipation; then come the breathtaking bursts. Old men's art dazzles as if new. New magic joins its splendor.

Making the boom fit the beat

WHEN the crowd sings ``the rockets' red glare,'' the sky, of course, is supposed to explode in a blaze of scarlet. But synchronizing the boom to the beat is no easy task. For sound and color to coincide, the weight, the thrust, and effects of each shell must be calculated in advance, and launching cues written into the shooter's script.

Today, with computer programs that perform calculations in a split second, the ancient art of choreographing fireworks is becoming more sophisticated.

At one of the country's top pyrotechnics companies, Fireworks by Grucci, in Bellport, N.Y., the effects desired for each fireworks show are entered into a computer as the show is choreographed. A computer program generates a list of shells and mortars, a blueprint indicating where they are to be placed, a timing code and written script for the shooter, and a truck packing list for the warehouse.

Few other fireworks companies use such advanced technology - yet. But most use far more technology than a decade ago. Large shows are typically shot from an electronic firing board, which has 200 to 600 buttons.

Shooters listen by headphones to a music tape that has computer-generated timing cues overlaid to help them stay in sync with the music.

George (``Boom Boom'') Zambelli anticipates prepackaging Zambelli Internationale's rendition of popular numbers, such as ``The Stars and Stripes Forever'' and ``The 1812 Overture.'' A town would receive in the mail a package containing the musical tape, the shooter's script, the fireworks themselves, and the equipment to detonate them.

Technology now being developed would link a personal computer to a videodisc and display screen. As a show is choreographed, the screen will present images of bursting shells, previewing the show.

But with all their speed and precision, computers are no substitute for creativity. Philip Butler, marketing manager of Fireworks Grucci, sniffs, ``Did Michelangelo need a computer to create his works?''