This winter, when the wrecker's ball crashes into the red brick walls of the American Mosaic Co. at 912 I St. NW, it will wipe out more than just another rowhouse.

The falling walls will shatter an intricate terrazzo floor laid with pride by Romero DiGiulian's father 70 years ago, and with it, DiGiulian fears, much of his business as well.

Six blocks northeast of the White House, on the three-block site surrounding his building, the District of Columbia plans to build its long-heralded convention center -- a nine-acre, two-story trapezoid designed to lure tourists, jobs and money to a rundown section of the inner city.

Where DiGiulian now stores fine marble and granite in a skylit workshop, the National Solid Waste Management Association -- the center's first scheduled customer -- will convene in three years to talk about trash.

DiGiullian, a shy man who appears to be about 60 but refuses to give his age, is reluctantly preparing to move the family business from downtown Washington to suburban Maryland. But he's shaken by the prospect.

"My life is here," he said. "I came here as a child to watch my father work and now I've worked here for 40 years."

More than sentiment, however, is involved. The family had paid off the mortgage on the building shortly after World War II, and rent from three apartments above the office covered taxes on the property.

Last January, the city took the property by eminent domain. He and the city are still arguing over the right price, DiGiulian says, but meanwhile he's having to pay the city $1,200 a month rent which he says requires him to triple his business just to stay even.

In the suburbs, he says, he'll have to pay even more. In addition, he'll be far removed from the embassies and federal building where he does most of his business.

A year ago when Congress finally made the convention center a reality, 71 small- and medium-sized businesses were given notice to leave the three-block area. The 19th and early 20th century buildings housed churches, restaurants, bars, book stores, a clothing store, an optical company, a printing company, a camera store, a branch of the Salvation Army as well as the mosaic company.

Official city figures show 17 firms went out of business rather than risk a move to a new location with higher rents. Five have left the District and 30 remain on the site bounded by 9th, 11th and H streets and New York Avenue NW.

DiGiulian and other business owners interviewed say they have been frustrated in their attempts to find new locations in the city are weary of city paperwork required for them to receive cash for their business losses.

"I'm sick of fighting," says DiGiulian. "I've got to get the hell out but I've got to figure out how to move tons and tons of marble and granite as well as my polsihing and cutting machines."

City officials involved in the relocations and demolition project say they are not unsympathetic to the trauma the moves have caused. The convention center, they are quick to point out, has been mandated by the City Council and they are simply the people who must see the site cleared.

"We're not heroes," said James Woolfork of the D.C. Department of Housing. But "over all, we're pretty pleased with out relocation efforts."

A block north of the mosaic company in the six-year old Dante Office Supply Company at 930 New York Ave. N.W. manager Patty Cox yells, "Don't ask me about moving! Don't ask me about the D.C. government!" Waving a file of government forms. She says "We're moving because of garbage like this. We begged them for help and all they gave us was a list of locations in Maryland and Virginia. Ninety percent of our business is in downtown and yet we're forced to move to McLean," she said.

Cleveland Herring owns the tiny For Ward Liquor Store at 805 10th St. NW. He has been in business for two years.

"I only pay $150 to rent this space and that's how I can make money here. The places I've been shown in the area rent for $500 to $2,000 a month. If the government can't subsidize my rent, I'll have to close down," he said.

Ivan Hall, a watch and clock repairman has worked at 807 11th St. for 30 years. Surrounded by ticking, chiming, cuckooing clocks.

"The city has found me a place a block south of here but that would be a temporary place. They're supposed to tear that building down in two years. You know, it would take me two years to get everything arranged so that I can do my work," he said.

For 45 years, Joseph Rappaport has run his Bargain Book Store at 808 9th St. NW. From his platform at the front of the store, he can watch his customers look over the 10-cent, battered paperbacks and the new, hardcover books marked at half price.

"I don't feel like starting fresh somewhere else," he said. "I'm afraid I'd lose my customers if I left the area."

As he took money for a car repair manual, he said the convention center "will change the whole character of the city. Small businessmen like me can't make it with those high-rise building and those high rents," he said.

"We will begin demolition of those buildings the first of the year," said D.C. Housing's Woolfork. "Our groundbreaking is scheduled for April of 1960."

Woolfork and other Housing staffers maintain that they are doing much more than required to help the businesses and residents of the convention center area relocate.

"We have opened an office (on New York Avenue) to counsel displaced persons as to their rights and to help them find new facilities which are within their budget and meet the D.C. housing code," said Woolfork.

Woolfork also said that business owners are entitled to moving expenses, replacement value of unmovable property such as special built-in machinery or a cash settlement of $2,500 to $10,000 in place of the moving and replacement costs.

The housing official said that the people of the convention site area who claim the city is doing nothing to help them, actually mean that the city has not been successful in helping them. "Our task is to help them in spite of themselves," he said.