ROTTERDAM — Pronounced declines in Rotterdam’s share of the county sales tax and a marked decrease in mortgage tax receipts are starting to have an impact on town coffers.

Comptroller Patrick Aragosa said Rotterdam is receiving about $23,000 less per month than the town was allotted by Schenectady County the previous year. He said the decrease in revenue is throwing a wrench into the 2008 budget and is likely to prompt town officials to tap the town’s $3.5 million fund reserve this year.

“We’re off,” he said. “We’re getting a smaller cut this year.”

Aragosa said Rotterdam received $211,000 per month in sales tax in 2007. In contrast, he said the town was allotted $187,000 per month when county officials released the sales tax apportionment in January.

“But it was too late at that point,” he said. “Our budget was already set.”

Sales tax revenues are one of the town’s primary revenue sources. Schenectady County guarantees $7.7 million in sales tax revenue to be divided among the towns of Glenville, Rotterdam, Niskayuna, Princetown and Duanesburg, as well as the villages of Scotia and Delanson. The city of Schenectady has a separate sales tax agreement with the county.

Each town or village receives its guaranteed share proportionate to the full value of its property. Municipalities with a greater total property value receive a larger percentage of the sales tax.

County Finance Commissioner George Davidson said Rotterdam’s cut of sales tax revenue could have dropped only because the town’s property didn’t increase in value at the same rate as other municipalities in the county. Without an equal or greater growth total valuation, he said, Rotterdam’s percentage of the sales tax revenue would dip.

“If that value was less in relation to all the other towns the year before, that’s the only way they would have gone down,” he said.

Prior to last year’s revaluation, Rotterdam had an equalized value of $2.32 billion, according to the state Office of Real Property Services. This value increased to $2.51 billion in 2007 and $2.63 billion in 2008, for a total increase of about 4.7 percent.

Property in all of the county’s towns and villages was valued at about $6.12 billion in 2006. This figure jumped to $7.27 billion in 2007 and $7.66 billion in 2008, an increase of about 5.2 percent.

Proponents of last year’s revaluation in Rotterdam argued the town wasn’t receiving its fair share of the sales tax revenues because its properties were assessed on a fractional basis. By bringing the town’s equalization rate up to 100 percent, they argued underassessed properties in the town would be brought to full value, thereby allowing Rotterdam to collect a greater percentage of the sales tax revenue.

Instead, the reassessment appears to have had either a negative or negligible effect on the apportionment. Aragosa said the town is now trying to get to the bottom of the shortfall.

However, Davidson said fluctuations in the sales tax apportionment aren’t uncommon from year to year. While admitting these fluctuations can cause budget problems for local officials, he said Rotterdam’s sales tax shortfall will likely be balanced by the town having to pay less toward the county’s property tax levy.

“From a residential standpoint, it probably works out better,” he said.

Meanwhile, Rotterdam officials will also need to contend with the cooling Capital Region housing market, which has prompted a downward trend in mortgage tax receipts. Aragosa said the town is short about $75,000 in budgeted mortgage tax revenue.

Overall, Aragosa said the town budget anticipates $753,000 in mortgage tax for the year but has collected only $350,000 over the first two quarters of 2008. This figure is significantly less than the $465,000 collected during the first two quarters in 2007.

“We’re at a tough spot,” he said.