Idaho's hydroelectric dam developers are blaming the Idaho Tax Commission for property tax assessments that have risen an average of 40 percent in the past year.

Rising property tax bills have prevented two or three developers from pursuing projects, although they have obtained licensing from the Federal Energy Regulatory Commission, one industry spokesman said.But Tax Commission officials say the higher rates reflect the true market value of those operations, and if the rates had not been increased, then other property owners would have been forced to pick up the slack.

The same 1987 legislation that triggered the simmering dispute between the commission and Idaho's cable television companies is at the heart of the hydroelectric development argument.

"It's two horns on the same goat," said Vern Ravens-croft, a former state legislator and candidate for governor who constructed a hydroelectric plant at Good-ing in 1984. He is among 22 of the state's 59 private hydroelectric plant owners who have filed suit against the state Tax Commission.

The assessment process began in 1987 when lawmakers placed the hydroelectric industry and cable television under the assessment authority of the tax commission. This year, the state's hydro plants were valued at about $80 million.

Cable TV operators, aware the commission planned to increase their property tax values substantially, persuaded the Legislature to restore that industry to the jurisdiction of county assessors.

However, the commission directed assessors to apply new methods that produced dramatic increases in the assessed tax value of cable television systems.

Hydroelectric developers opted to remain under the review of the commission. Even now, they are not challenging the commission's authority to make the assessments, only its methods.

"In our case, it's strictly a court challenge," Ravens-croft said. No effort will be made in the 1989 Legislature to strip the commission of its authority to assess hydro plants, he said.

One reason for that may be the fact hydro project assessments had been climbing gradually even under the county assessors. The 40 percent increase also pales in comparison to the assessments applied to cable TV companies, which jumped in some cases by 1,000 percent.

Instead, the hydro operators, who secured the right to sue by challenging the assessments first through the tax commission's administrative appeal process, mounted a lawsuit last fall aimed at the tax commission's appraisal methods.

"I think they are applying their appraisal process with a great deal of inexperience and without taking into consideration some of the questions of uniformity," Ravenscroft said.

Industry officials say the commission's eight-month-long assessment review process does not give plant owners a depreciation allowance, but Tax Commission officials counter that the plants will grow in value with demand for electricity.

"We have to have a fair and predictable tax structure if we're going to encourage investment in this state," said Boise attorney Stephen Beane, who represents the 22 hydro plant owners.