Manhattan prosecutors have executed a search warrant at a company that supplies concrete to large public works projects in the city, marking a significant expansion of a 17-month investigation in the concrete testing industry that they say has exposed widespread fraud, according to court papers and officials.

The search took place on Aug. 6, and a day later the city's Department of Transportation banned the company, the Casa Redimix Concrete Corporation, from serving as a supplier on a major venture, the $612 million replacement of the Willis Avenue Bridge, which spans the Harlem River.

The company won a temporary restraining order in State Supreme Court on Friday, allowing it to continue work on the bridge pending a hearing next month. A lawyer for the company said it had done nothing wrong and defended its work.

The search of Casa's offices, on Edgewater Road in the Bronx, was conducted by the office of the Manhattan district attorney. Court papers filed by the city in its effort to suspend Casa said the company was a subject of the continuing inquiry into the concrete testing industry, and the company acknowledged the search in its response.

The investigation, begun in March 2008, has resulted in charges alleging a series of crimes, including the failure to perform some required tests and the fabrication of the results of others on scores of construction jobs, including Yankee Stadium, 1 World Trade Center and other prominent projects.

Concrete testing, required by the city's building code, is viewed as a basic safety measure. Faulty concrete would be less durable and not last as long. Investigators, industry experts and engineers have said they do not believe any falsified tests created immediate hazards, because most of the concrete poured in New York is of high quality.

The investigation has been a source of embarrassment to the administration of Mayor Michael R. Bloomberg, a forceful advocate of development in his two terms. The construction industry has presented a series of problems for the mayor, among them a rash of deaths and accidents, including two fatal tower crane collapses in 2008 and the deaths of two firefighters at the former Deutsche Bank building in 2007.

Facing criticism of the city's oversight, Bloomberg has instituted regulations and signed legislation, but problems persist at the Buildings Department, long plagued by corruption and mismanagement. A year after the agency announced that it had a plan to retest concrete in an untold number of buildings in response to the investigation, few checks have been done and the agency refuses to make its plan public.

The inquiry has led to the indictment of two companies. State racketeering charges have been brought against the largest in the region, Testwell Laboratories, and several of its officers and employees. Another company, Stallone Testing Labs, and its laboratory director have been charged with fraud.

A third company, American Standard Testing Laboratories, has acknowledged that it is under investigation. The defendants in the two criminal cases have pleaded not guilty, and American Standard has denied wrongdoing.

The search of Casa's offices, where the authorities seized three dozen boxes of records and a computer, suggests that investigators have begun to focus on companies beyond testing laboratories, a significant broadening of the inquiry. Several people briefed on the matter said additional suppliers and other companies were also facing scrutiny, but did not name them.

When the charges against Stallone were announced at a news conference last month, the district attorney, Robert M. Morgenthau, and an aide suggested that the inquiry would widen.

Morgenthau said prosecutors had seized faxes and e-mail messages from Stallone indicating that contractors were knowingly buying false test results. The records, he said, showed that contractors ordered overnight mix design reports with test results that were supposed to take 28 days.

Patrick Dugan, the office's chief of investigations, said at the time that investigators were identifying the contractors who received those reports and results. "That's the next chapter," Dugan said.

Several people briefed on the matter said one of those companies was Casa.

The State Supreme Court justice who blocked the city's effort to suspend Casa, Alice Schlesinger, wrote in her decision Friday that there was no information beyond the execution of the search warrant that the company had violated the law and that unsafe concrete had been used.

She said, however, that "in order to insure the safety of the public," the city and the company building the bridge, a joint venture of Kiewit Construction and Weeks Marine, "have complete authority to monitor and supervise in accordance with their own judgment."

A lawyer for Casa, William B. Wachtel, said the company, like other concrete suppliers, sells mix designs for which tests have already been performed, essentially taking a standard recipe for a certain strength of concrete off the shelf. Casa rarely deals with the testing companies, Wachtel said.

"Concrete suppliers are like pharmacists," he said on Friday. "They fill the prescriptions that contractors issue and nothing more."

Casa's owner, Mauro Perciballi, denied wrongdoing in a sworn affidavit filed as part of its effort to block the suspension and said that neither he nor Casa had ever "been accused, much less convicted, of a crime." He said that roughly 80 percent of the company's work was on contracts performed for the Department of Transportation and other city agencies; it supplied concrete for the Third Avenue Bridge, the 145th Street Bridge and Interstate 95.

For nearly two years, Perciballi said, Casa has supplied concrete "In particular, there have been no complaints or reported deficiencies with respect to the concrete Casa has provided to the project," he said. "In fct, it is my understanding that the concrete provided by Casa to the project has routinely tested at strengths well above the required specifications."