A small group of Montgomery County taxpayers last week appealed a decision by the Maryland Tax Court upholding the state's controversial triennial assessment program, claiming that the tax court erred in its findings and "illegally" attempted to settle constitutional issues outside its purview.

A three-judge panel of the tax court, the highest administrative review board for tax issues in Maryland, ruled Sept. 17 that the state's assessment program did not violate the state's constitutional requirement for uniform assessments.

The group of seven taxpayers first challenged their assessments before the county Property Tax Assessment Appeals Board in 1980, charging that because their homes were among the first to be assessed in 1979 under the new program, they paid higher taxes than owners whose property was assessed in the second and third years of the implementation of the program.

The county board supported the landowners, but subsequently said it had no authority to decide whether the state assessment system was constitutionally valid. The case was then appealed to the tax court.

The triennial assessment system divides properties into three groups and reassesses each group once every three years, phasing in the increase in value over the following three years. Several of the landowners charged that they paid as much as $900 more in taxes on their property because it was in the first group than landowners paid on similar properties in the third group.

In the September decision, however, the tax court upheld the state's program, saying that "temporary disparities among properties under a cyclical assessment system are inevitable," and that they "do not render the system unconstitutional."

The taxpayers, however, claim that the tax court made 19 errors in its decision, including the error of failing to find "that appellants' properties' assessment levels were adversely affected by the triennial assessment system."

In a petition for relief and a notice of appeal filed in Montgomery County Circuit Court last Friday, the landowners have asked that the court reverse the tax court's decision and that they be treated in the same fashion as the most favored group of landowners, those assessed last under the state's new program.