Nassau County used a new and untested method for assessing residential properties that will shift the overall tax burden to middle-class homeowners while reducing taxes on high- and lower-end homes, County Comptroller George Maragos says in a draft audit.

According to the draft, obtained by Newsday, the new method will increase the overall property tax bills of owners of middle-range homes by an average of $227 each next year; owners of top-end houses will see an average tax decrease of $173, while owners of the least costly houses will see a drop of $55 on average.

According to the draft, the county dropped the use of comparable properties in determining the tentative residential assessment roll issued this January and affecting 2012-13 tax bills. Nassau instead used the lowest of an array of values - including last year's assessed value, any reductions resulting from property tax protests or a recent sale of the property.

The draft does not detail the range of assessments of the homes grouped as top-end, middle-range or low-end.

County Executive Edward Mangano has not seen the draft or its findings, said spokesman Brian Nevin. "This information is unfounded," Nevin said of the draft report's findings. To his knowledge, he said, nobody in the administration has seen it.

But Maragos' office, which has refused to release the draft, said last week that it had been sent to the administration for comment.

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Comptroller spokesman Jostyn Hernandez cautioned that it is still subject to change. The comptroller will correct any factual errors the administration may raise and also include the administration's response to the report's findings.

"The comptroller's office does not comment on draft reports," Hernandez said. "The audit . . . is a work in progress and as soon as it is final the comptroller will make it public and discuss the findings. In general, all of the numbers and information in our draft reports go through a rigorous . . . process to test the accuracy of the data before official release."

The audit is critical of assessment procedures before and after assessor Ted Jankowski was fired in October in the wake of complaints from town officials about mistakes in the new school assessment roll and an erroneous $1.3-million school tax bill for the historic county courthouse in Mineola. Maragos announced at that time that he would conduct an audit of the assessment roll.

The audit quotes an e-mail from the former assessor dated Nov. 24, 2009, to a former deputy saying, "Hey, if I can sell the quality of our residential values with a straight face I can sell anything - strategically a step we had to take though - however sometimes I feel like a snake oil salesman."

Jankowski responded Tuesday, "It sounds juicy, but without knowing the full context I can't imagine writing it. Our data and an independent Newsday study showed that residential values weren't as bad as they were being portrayed by those seeking financial or political gain by misrepresenting them."

Auditors said the new assessment method is not used by other municipalities, was not reviewed by mass-appraisal experts and has not been tested to see if it complies with state law. The assessment roll "produced by the new and unvalidated methodology appears inequitable, will shift the tax burden to midrange-valued homes and may increase the number of property owners filing grievances," they said.

The change has raised complaints from some homeowners. Steven Hirsch of Great Neck, who last year found errors on the county website, said he cannot make sense of the new method as described on the site.

"It's Greek," Hirsh said, "I think [it] is being used to play some sort of games with our appraisals." He noted that his home's value of $613,000 was unchanged while the value of a friend's house in Port Washington inexplicably dropped by 15 percent.

Hernandez predicted the audit will be released at the end of the month or early next month.