At the same time, federal and city officials have not made public the precise number and location of the buildings involved, or disclosed specifics of what they think took place in each instance. While the city’s health department has reviewed 17 cases in which Mr. Todaro performed lead tests, it remains unclear whether city officials plan to conduct any other reviews or retesting.

But the stakes are unquestionably high.

The Environmental Protection Agency has found that the long-term effects of lead exposure in children and adults can be severe. Inhaling asbestos can cause lung disease and cancer.

Several city agencies sought to play down the dangers.

City regulators have found no evidence that either the fraud or risks are widespread, said Marc La Vorgna, a spokesman for Mayor Michael R. Bloomberg.

“We can always look for new ways to improve our process,” he said. “D.E.P. is going to start increasing audits, which is the right step to ensure inspections are being completed properly.”

But, in addition to the continuing investigation that grew out of the charges against Mr. Todaro, there are now six other unrelated federal cases under way exploring allegations of similar practices in the New York City area. Some 1,500 people hold city or federal certifications to test for lead or asbestos in the area.

One line of inquiry for investigators in the case involving Mr. Todaro is whether any building owners, management firms or contractors for whom he or other inspectors worked paid bribes for the bogus inspection reports. Officials say substantial sums of money could have been saved by allowing the demolition of buildings without performing expensive asbestos abatement.

Indeed, several current and former law enforcement officials and industry experts underscored that the city’s construction industry, and in particular the demolition and asbestos abatement sectors, have a rich history of corruption.