Manhattan prosecutors are expected to seek state racketeering and fraud charges later this month against about a dozen officers and employees of a company hired to test the strength of the concrete at some of the biggest construction projects in the New York area, according to investigators and others briefed on the case.

The charges are expected to accuse the company’s president and several senior officials of failing to do some tests and falsifying others over a period of about five years, the investigators and the others said. They spoke on the condition of anonymity because no charges had yet been filed.

Prosecutors are also expected to ask the grand jury convened in the case to vote enterprise corruption charges  the state equivalent of federal racketeering violations  against the company, Testwell Laboratories Inc., along with some of the company’s senior officials, with lesser charges leveled against other employees, the people briefed on the case said.

When the investigation was disclosed in June, after prosecutors executed search warrants at Testwell’s headquarters in Ossining, N.Y., lawyers for the company vigorously defended its work and said its officials denied wrongdoing. They said that tests had been done properly and that company officials had cooperated with the inquiry.