BOSTON — Francesco Insolia, president of a New Bedford manufacturing company raided last year by immigration agents, yesterday pleaded guilty to harboring and concealing illegal immigrants, a criminal felony charge that could land him in prison for 18 months.

But the plea agreement will spare Insolia a maximum 10-year sentence and more than $600,000 in fines.

Insolia, founder and former president of Michael Bianco Inc., quietly stated “guilty” in U.S. District Court to an information charge of harboring and concealing illegal immigrants by allowing the company to submit false Social Security numbers for employees to the government. The charge says he did so for “commercial advantage and private financial gain.”

The Bianco company (MBI) also pleaded guilty to 18 specific felony counts of knowingly hiring illegal aliens; helping to harbor and shield illegal aliens from detection from authorities; failing to pay them full overtime; Social Security fraud; and mail fraud, “all in an effort to maximize profits on a series of lucrative military contracts,” said U.S. Attorney Michael J. Sullivan. The counts involve the period between early 2004 and late 2006, a time during which the company grew from fewer than 100 employees to more than 600.

Insolia, 51, of Pembroke, Mass., has agreed to serve 12 to 18 months in federal prison and pay a $30,000 fine. The company has agreed to pay a $1.5-million fine and $460,000 in restitution for overtime wages owed to its employees.

U.S. District Judge Douglas P. Wood-lock set sentencing for Jan. 27.

Insolia afterward gathered with family and friends. Frank J. Libby Jr., lawyer for both Insolia and MBI, declined comment.

“Employers who knowingly hire an illegal work force exploit illegal aliens, take jobs away from legal workers and gain an unfair advantage over their competitors,” said Julie L. Myers, Homeland Security assistant secretary for Immigration and Customs Enforcement. “It is not OK for business owners to line their pockets by breaking the law. The pleas today reflect the type of employer ICE targets during our worksite enforcement investigations.”

The charges stem from a March 6, 2007 raid in which ICE agents arrested 361 suspected illegal immigrant factory workers, primarily from Guatemala, Honduras and Mexico. The workers were helping fulfill more than $230 million in government contracts for rucksacks, ammunition pouches and other survival gear for U.S. troops in Iraq and Afghanistan.

The raid sparked widespread public outcry: advocacy groups, social service agencies and public officials decried a “humanitarian crisis” that disrupted the lives of families. ICE disputed the allegations.

Insolia and his top managers were indicted last year on conspiracy charges related to the hiring of illegal immigrants, and knowingly harboring them for purposes of executing the company’s military contracts. But in August, the sides hammered out a plea agreement that led to the single criminal felony count against Insolia, and the felony counts against his former company.

His codefendants entered guilty pleas last month. Dilia Costa, the Bianco company’s production manager, pleaded guilty to hiring and harboring illegal aliens. The company’s contracts administrator, Gloria Melo, pleaded guilty to one count of continuing to employ illegal aliens even after the company had reason to know they were illegal.

Assistant U.S. Attorney Donald Cabell yesterday outlined evidence the government would have presented against Insolia and the Bianco company, if the case had gone to trial.

Cabell said a Dec. 5, 2005 immigration raid at another New Bedford plant should have made Insolia aware that undocumented immigrants were working at his company — if he didn’t know already.

That day, ICE agents “conducted a surprise inspection at a New Bedford fish-processing plant across town,” Cabell said, after which workers there “called friends and relatives by cell phone” at the Bianco factory, warning them that ICE could be on its way. Many workers then fled the Bianco plant, said Cabell.

“At some point that day, Mr. Insolia discovered that some or many had left — and he knew, or should have known” that undocumented workers were in his employ, Cabell said.

“But he allowed the company to submit Social Security numbers to the IRS and the Social Security Administration, knowing that many were false … to allow them to stay at a time when they were needed” to fill government contracts.

Cabell said the government would also prove that the Bianco company “committed a number of acts that allowed illegal aliens to remain concealed,” including that bogus IDs were knowingly treated “as legitimate,” and that in some cases workers “were directed to individuals outside the company who were known to provide false documents.”

After the raid, workers alleged that Insolia and his managers had exploited them and subjected them to poor working conditions, including fining them $20 for such “infractions” as spending more than two minutes in a restroom stall or talking while working. Workers also said Insolia kept a back exit door locked, did not adequately heat the building in winter or cool it in summer. The company later agreed to pay a $37,500 fine after the government cited Bianco for numerous serious workplace health and safety violations.

ICE spokeswoman Paula Grenier said that since their arrests last year, 168 detainees were returned to their home countries; 116 have cases pending before the immigration court or the board of immigration appeals; 26 are under a final order of removal from the U.S.; and 16 “were granted either a benefit or a relief from the immigration court.”

Michael Bianco Inc. sold the New Bedford plant last year to Eagle Industries, a longtime Bianco competitor based in Fenton, Mo.

kziner@projo.com