Philadelphia's Board of Revision of Taxes ruled in favor of a parking lot owner at a hearing this morning, cutting the owner's property tax bill 44 percent by applying an assessment ratio established last summer by a state board that reviews property taxes.

The ruling in favor of Race Street Parking Associates has significant implications for the budgets of the city and the school district because owners of nearly 1,000 properties representing about 60 percent of the city's nonresidential property base filed similar appeals.

Based on those pending nonresidential appeals, the revenue loss to the city and the struggling school district could be as much as $80 million.

Board of Revision of Taxes chairman Judge Alan Silberstein said the board was simply following the law. "We feel its our duty as a board to protect the citizens of Philadelphia, so everyone pays a fair share," Silberstein said after announcing the decision.

The city will appeal to the Court of Common Pleas, said Frances R. Beckley, chief counsel to the city's revenue department. But, Beckley declined to discuss the city's strategy beyond that.

The first appeal ruling today was based strictly on a decision last summer by the State Tax Equalization Board, an agency in Harrisburg responsible for the quality of counties' assessments.

Using data sent by each county, the state board calculates the accuracy of assessments by comparing actual sales prices each year to assessment values. The figure it publishes from those calculations is called the common level ratio.

In some counties, including Philadelphia, property tax is calculated on a percentage of the official market value. That percentage is called the predetermined ratio. In Philadelphia, it is 32 percent.

If the common level ratio calculated by the state tax board differs by more than 15 percent from a county's predetermined ratio, then the state board's ratio must be used when a taxpayer files an appeal.

The state tax board determined last summer that the city's common level ratio was 18.1 percent, opening the door for appeals based solely in that number.

In the first case decided today by the Board of Revision of Taxes, attorney Joseph C. Bright, of Cozen O'Connor, said his client should only pay taxes on 18.1 percent of the market value of five parking lots, not the 32 percent used by the city. He said his client agreed with the market value.

In a bid to save revenue, the Philadelphia School District tried to appeal the market value of those parking lots, as it did every other case where the property owner wanted the 18.1 percent ratio applied.

The Board of Revision of Taxes rejected the school district's effort to open up the market value in the case. "We intend to apply 18.1 percent to the market value," Silberstein said.

Relatively little money was at risk in the parking lots case, just $30,363 in reduced taxes, but the significant implications were quickly apparent.

In a second case involving the common level ratio the property owner had initially appealed the market value of the former DisneyQuest site on the 800 block of Market Street and had asked for the application of the 18.1 percent common level ratio to the new market value.

Judge Silberstein gave the attorney, Carl S. Primavera, the opportunity to withdraw his appeal of the market value and simply accept the 18.1 percent common level ratio. That will reduce the property tax on the parcel, now a parking lot, by $159,733.