Allegheny County's 2002 "base year" property assessment system is going on trial.

In a closed-door meeting with attorneys yesterday, Common Pleas Judge R. Stanton Wettick Jr. set Dec. 11 as the start date for a legal battle over whether the county's decision to stick with 4-year-old assessments violates the Pennsylvania Constitution. His eventual ruling likely will have implications for how every county in the state assesses property value.

Two groups of homeowners have sued Allegheny County, arguing that the base year places an unfair tax burden on properties with falling or stagnant values.

The judge yesterday also scheduled a hearing next Thursday in a separate lawsuit, filed by a Wilkinsburg couple, that claims the county's assessment appeals board must consider current market values, even under the base year.

"I think Judge Wettick realizes this is a problem that is bigger than Allegheny County," said Charles McCullough, a former county solicitor who now represents Upper St. Clair and Upper St. Clair School District. "He wants to get this settled once and for all."

Mr. McCullough's clients, along with dozens of other school districts and municipalities, have taken a keen interest in the progress of the lawsuits. Millions of dollars in potential tax revenue is at stake.

County Chief Executive Dan Onorato last year put a halt to regular reassessments, saying the process was too flawed and unpredictable to create fair values for more than 500,000 residential properties. Instead, he and County Council adopted 2002, the year of the last full reassessment, as a base, meaning property owners won't see any changes for years to come. It's a practice used by neighboring counties.

In March, Judge Wettick ruled that state law permits the base year approach, and the two groups of homeowners then decided to mount a constitutional challenge.

Donald Driscoll, an attorney representing homeowners from Braddock and the Hill District, had asked for a ruling without a trial, but Judge Wettick yesterday told lawyers involved with the case that he wanted as many facts as possible to be on record since any decision likely will be appealed.

Mr. Driscoll said he will call expert witnesses who can explain how the base year is heightening tax inequality among property owners in Allegheny County.

"The impact of this on specific homeowners is very significant," he said.

One client, Kenneth Pierce of Braddock, said he would eagerly testify on his own situation. He argues that his Camp Avenue property's $27,900 assessment is artificially high under the base year system.

"[Onorato] sure didn't help me," Mr. Pierce said. "My taxes were raised. They doubled."

County Solicitor Michael Wojcik said he didn't think the testimony of individual homeowners would be relevant in the trial. The county, he said, will present experts on the history of the base year system, which the state Legislature created in 1982 as an alternative to regular reassessments.

Some counties haven't conducted a new assessment in decades. Blair County, for instance, last assessed property in 1958.

Next Thursday, Judge Wettick will hear arguments in a separate lawsuit filed against the county and the seven-member appeals board. The plaintiffs, James P. and Jennifer Daugherty of Todd Street in Wilkinsburg, bought their home in 2004 for $31,500, although their property's assessment is stuck at $66,900. They claim that state law allows them to file an appeal using current market value to win a reduction.

Appeals board members are hoping for a quick decision in the case because they have already started hearings for thousands of homeowners.

This week the board also started hearings for more than 11,000 property owners who bought their homes after 2002 and saw school districts or municipalities win assessment increases. The county has filed new appeals on behalf of those residents in an effort to reverse the increases and bring them in line with the base year.

At next Thursday's hearing, Judge Wettick also will consider whether taxing bodies can present recent sales prices as evidence of a home's value in 2002 when going before the appeals board.

Martin W. Sheerer, solicitor for the Fox Chapel School District, worried that the judge's ruling in either lawsuit could upend results from thousands of appeals.

"There's enormous interest by all school districts," he said. "There's a great chance that all the time and expense that went into [appeals] could be wasted."