A Washington Post story on July 5 incorrectly reported that the Metropolitan Washington Board of Trade had paid part of the cost of this year's Fourth of July fireworks show on the Mall. In fact, the Washington Area Convention and Visitors Association, not the Board of Trade, had contributed money to help pay for the show; the other contributors were the National Park Service, the D.C. Department of Recreation, and Government Services, Inc.

As time may labored with shovels and hammers on the west edge of the Washington Monument grounds yesterday afternoon, hardly a head was turned or an eyelash batted. But a few hours later, the labors of that same threesome - Joseph Zambelli, his son Anthony Zambelli, and helper David Barnes - would engage hundreds of thousands of rapt eyes, ears and noses, and provoke a chorus of "Oohs" and "Aahs" for miles around.

The Zambelli Brothers Fireworks Manufacturing Co. has been handling Fourths of July on the Mall since 1958. Joseph Zambelli himself has been in the business, which was founded by his father, for 60 of his 70 years.

In spite of his age and a bad case of arthritis, Zambelli has lost none of his enthusiasm for fireworks. "That's all I ever did, I love it," he said yesterday as he scurried around issuing orders to his two assistants, to National Park Service maintenance men, to Park Police officers, and to anyone else who happened to be in earshot.

This, Zambelli believes, should have been the Zambelli Brothers' 20th straight Independence night on the Mall - should have been, that is, except for the unpleasant matter (which Joe Zambelli would prefer to forget) of 1976, the Bicentennial year. The contract for the fireworks for that monumental year was let instead to a French firm with a reputation for unusually delicate, subtle displays.

Unfortunately, there were widespread grumblings that year that some of the displays were not only subtle but virtually invisible except to those lucky enough to find front-row seats. "Most of their displays were all eye-level," recalled the Park Service's James A. Rubin.

"Everyone at the Park Service was greatly disappointed," said spokesman George Berklacey.

Reggieri, the French firm, was paid $100,000 for its fireworks exhibition by "Happy Birthday, USA," a private group established to arrange Bicentinnial festivities here. "We would have done it for half, less than half," said Zambelli yesterday. "But the politicians, you can't beat them."

This year's fireworks, paid for by the Park Service, the D.C. Department of Recreation, Government Services, Inc., and the Metropolitan Washington Board of Trade, will cost $12,500, the same as 1977. Zambelli insisted his company would make no money at that price, but likes to do the Fourth of July show on the Mall for "advirtising!"

Zambelli and his crew drove down to Washington Monday from the company headquarters in Newcastle, Pa., and spent the night at the Hotel Washington. Yesterday morning, they were down on the Monument grounds bright and early with a U-Haul truck full of fireworks bombs - 93 different kinds, weighing about two tons altogether - and hundreds of firing-tubes.

There's no other company that's got as many pipes as we got." said Zambelli. "We're No. 1. We're No. 1 in America. All the best jobs, we have." A competitor recently protested that it was becoming impossible to compete, according to Zambelli - "He told me: 'Jesus, wherever I go it's all Zambelli."

Through most of yesterday morning, a Department of Interior backhoe - a vehicle resembling a motorized anteater - dug trenches under Zambelli's frenetic direction, while his two crew members carefully stood the firing-tubes up on end.

When he is not setting up displays, Zambelli runs one of the company's two factories, but younger brother George runs the company itself. "He's a big wheel," said Zambelli. He's a college man. He goes out and gets the bids. But if it wasn't for me, he wouldn't be where he is now."