Allegheny County Chief Executive Dan Onorato went on the offensive yesterday to push his proposal to cap property assessment increases at 4 percent for 2006.

Onorato, who does a monthly one-hour show with KDKA Radio's Mike Pintek, requested and received an extra show yesterday to talk about assessments.

He said calls and e-mails to his office have been overwhelmingly in favor of his proposal. But he acknowledged criticism from legal experts, former county officials and a state agency that analyzes the accuracy of assessments.

Onorato decided Tuesday not to mail out new assessment figures for 2006 because he had little faith in their accuracy and considered them too high. He has asked County Council to change the county administrative code to establish a cap of 4 percent on increases, including 17,000 properties where assessed values would have doubled.

"If I let these numbers go out, there will be massive tax increases across the county," Onorato said, stressing that after similar reassessments in 2001 and 2002 a substantial majority of school districts and municipalities didn't decrease property tax rates to offset additional revenue.

"It's too easy to take the revenue. Right now, I'm bringing some sanity to the system."

Critics claim that by refusing to implement the full amount of new assessments, Onorato's plan is regressive, shifting a greater burden to people with less-expensive homes.

Onorato countered that any break on expensive homes would be balanced in part by the $15,000 homestead exemption for county taxes, which is a greater benefit proportionately to those who own less expensive homes. He has called for extending that exemption and the senior citizen exemption of $30,000 to municipal and school taxes.

The homestead exemption shields the owner from taxes on the first $15,000 of taxable value, so all homeowners get the same break -- for this year, a $70.35 county tax reduction.

With more than 500,000 properties across the county, Onorato said it is too difficult to examine each for an assessment and there aren't enough sales each year to rely on computer models to make accurate comparisons. He is developing a formula to place properties into one of six categories: assessment decrease, no change, or increases of 1 percent, 2 percent, 3 percent or 4 percent.

Onorato said it wouldn't be practical to implement the figures as presented, which would result in an aggregate increase of 20 percent across the county, and let homeowners challenge assessments they consider to be too high. When the county did that in 2001 and 2002, it resulted in more than 90,000 appeals each year.

Onorato said his cap proposal would allow a reasonable increase in property values for tax purposes.

"At least I'm giving [school districts and municipalities] an increase to cover inflation," he said.

He acknowledged the new assessments fall within accepted guidelines for the real estate industry but said that's only the average. In reality, he said, too many properties are incorrectly assessed too high or too low, causing it to balance in the acceptable range.

Although he criticized the assessment system, Onorato said he considers Allegheny County markedly better than some surrounding counties, where values are changed only when a property is sold.

"We're the closest thing to reality in southwestern Pennsylvania," he said. "We're probably closer than anybody. But nobody gets it right and we're not going to get it right either."

Len Schockling, a Realtor with RE/MAX in Swissvale, said his experience selling homes in Swissvale and East Pittsburgh supports Onorato's assertion that the figures aren't accurate even in less-affluent communities. Preliminary numbers released by the county show assessments over the past three years increasing 16.34 percent in Swissvale and 14.94 percent in East Pittsburgh.

"Property values in East Pittsburgh have not gone up 15 percent in the last three years. No way," he said.

Onorato also renewed his call for the state to eliminate the use of property taxes to fund school districts.

Onorato expects to have a bill ready for County Council in the next two weeks to cap the assessment increases.