What public officials are characterizing as an "honest mistake" in determining the equalization rate for properties throughout Nassau has thrown local school districts into a state of absolute uncertainty about their own tax levy for this coming year.

Initial estimates from the Nassau County Assessor's office suggest that the school tax bill for residential homeowners in this area could be up to $100 more than had previously anticipated. In all 34 of the county's 56 school districts are likely to be affected in some way by this municipal accounting glitch.

The problem goes back to last December, when the State Office of Real Property Service in Albany issued tentative "equalization" rates for the four classes of property in Nassau.

These four classes are:

* Class One ¬ residential properties

* Class Two ¬ apartments and condominiums

* Class Three ¬ utilities

* Class Four ¬ factories, offices, and other business properties

Equalization rates are used in comparing the assessed values of property to market values. The purpose of the rates is to ensure that all properties throughout New York State are being measured on the same scale.

The process of determining the equalization rate and thereby establishing the tax rate has always been a cumbersome one, and this year, while going over the state's numbers, the Nassau Department of Assessment found a glitch: the rate set for two of the classes, Two and Four, were too low.

In March, the county successfully appealed the state's decision, and equalization rates for those two classes were raised as of April 22.

This move had the effect of shifting a greater share of the tax burden onto Classes One and Three.

The reason this became a problem for the districts _ and, evidently, a problem for district taxpayers in the long run ¬ is that while the error was being hashed out, school districts still had to adopt their proposed budgets for the year.

Because of the timing of Islandwide school district budget votes and board elections ¬ on May 19 ¬ districts had already mailed their residents budget brochures describing tax levies based upon the state's original equalization rates.

Though some districts did get word of the mistake prior to holding public meetings on their proposed budgets, efforts to explain the situation only served to confuse the issue further.

Now, local school administrators are left to explain the error and a tax rate higher than expected to angry residents. Worse yet, because the Department of Assessment is still analyzing the figures, school administrators are fielding telephone calls from taxpayers without having anything solid to tell them.

"I've already gotten 30 calls about the tax rate this morning, and it's only 8:30," said Sewanhaka High School District Superintendent George Goldstein. "The problem is I can only tell them exactly what I'm going to tell you now: we don't have any information yet that we can pass on to people."

The feeling of uncertainty in Sewanhaka is particularly intense because unlike most other school districts in Nassau, it has to rely on money generated by its component elementary school districts.

"In Sewanhaka, it's a domino effect," Goldstein said. "The way it works here, our four component elementary school districts tell us what their assessments are, and once they know their assessed valuation, we then determine what our tax rate will be.

"Our tax rate is predicated upon what their tax rates are," he explained.

Calls to each of the district's elementary school districts, Elmont, Floral Park-Bellerose, New Hyde Park-Garden City Park, and Franklin Square, proved equally unenlightening.

In Floral Park-Bellerose and Franklin Square, no one was available to comment on the situation.

In New Hyde Park-Garden City Park a secretary who answered the phone predicted that it would be a while before the district got word of what the new, and presumably real adjusted rate proportion for the district would be.

It was left to Jeffrey Carlson then, business manager for the Elmont Elementary School District, to sum up the situation facing all the local school districts.

"What will the tax rate be in the Elmont Elementary School District this year? The truth is, I don't know yet," Carlson said.

"We haven't gotten word yet, from the County Assessor's office, about how we will personally be affected by all this. Reports in the media thus far suggest that some districts will be more impacted than others. We just don't know where we fall.

"I hope to hear some answers regarding this situation some time this week," Carlson said.