TCI Cablevision of Lewiston has filed an appeal in 2nd District Court seeking an $18.7 million reduction in its 1988 property tax valuation.

Because of a change in assessment methods, the company's valuation rose from a total of about $1.1 million in 1987 to $19.5 million this year. The company wants the valuation reduced to $733,282.That amount is the company's estimate of its value based on an approach that considers the cost of tangible property minus depreciation. The higher amount is the result of an method that considers income, expenses and the value of the company on the open market.

In the appeal filed last week, the company charged that the valuation by the Nez Perce county assessor's office is "grossly excessive and unsupportable" and was not made according to recognized appraisal methods.

The cable company had asked the Nez Perce County Commission to reduce the amount, but the commissioners decided Dec. 2 to uphold the assessor's valuation. The tax due on that amount is $366,733.

County officials have defended the assessment, saying the Idaho Tax Commission ordered county assessors to appraise cable television property on the basis of the income it generates.

The order has stirred controversy elsewhere in the state. The tax commission has ordered 22 county assessors to appear before the commission next month to explain why they have not made substantial increases in their property-tax valuations for cable television companies.

If the commission concludes that the assessors improperly assessed the property, it can impose its own valuations.

TCI is seeking a court order barring the county assessor from assessing the company's intangible property, from using an income approach in valuing the company's tangible property and from seeking financial information other than items related to cost and accumulated depreciation of tangible property.