Acting Nassau District Attorney Madeline Singas' office said Monday that it will investigate the county social services department's rewriting of bid requirements that helped a longtime contractor stay on the job amid heavy competition.

Singas was responding to a Newsday report Sunday that detailed how small changes in the department's 2012 request for proposals for welfare fraud investigators all but eliminated six other bidders, four of which had proposed a lower cost.

Summit Security Services of Uniondale, which has provided welfare fraud investigators for Nassau since 2005 -- and in 2012 used several politically connected lobbyists -- was awarded the new contract. With renewals, it is worth up to $4.5 million over six years.

Story$4.5M contract's specs redone for firm's benefitDocumentOriginal welfare fraud investigators RFPDocumentsRevised welfare fraud investigators RFP

One losing bidder said the revisions to the welfare fraud investigations RFP -- including requiring membership in a professional organization that a Summit supervisor helped lead -- were designed to steer lucrative work to a favored vendor.

"This report is disturbing, and we are investigating this contract," Singas spokesman Brendan Brosh said in an email.

Social services officials have denied steering the contract. "DSS stands by the integrity of our contract process, and we welcome any external inquiries seeking further clarification for any of our more than 200 existing contracts," Commissioner John Imhof said Monday in response to the investigation.

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Singas, a Democrat who is running for election this fall, has made Nassau contracts a recent focus. In June, after Newsday reports, she issued subpoenas related to two contracts with retired NYPD Det. Richard "Bo" Dietl, who runs a private investigation firm, both falling just dollars below the $25,000 threshold that triggers scrutiny from the county legislature.

And last month, she issued a 35-page report on Nassau's contracting process, calling it a "recipe for corruption." The report was prompted by allegations that state Sen. Dean Skelos (R-Rockville Centre) and his son, Adam, improperly influenced the awarding of a $12 million county storm-water treatment contract to a company that employed Adam Skelos.

In addressing the RFP process, Singas wrote: "Skilled actors can often find a way to exclude unwanted competition."