Allegheny County Chief Executive Dan Onorato's efforts to create assessment values for 2006 hit a roadblock last night, when County Council narrowly put off a final vote on his latest proposal.

Earlier in the day, Mr. Onorato discarded a plan that would have led to average increases of 5.8 percent for the county's 500,000 residential properties. Instead, he asked council to establish 2002 -- the year of the county's last reassessment -- as Allegheny County's "base year," echoing a practice used by many nearby counties that haven't conducted full reassessments in decades.

"The uncertainty in the process will be removed," Mr. Onorato said alongside five of council's eight Democrats at an afternoon news conference, just two hours before council was scheduled to meet.

But Councilman Bill Robinson, D-Hill District, joined all seven council Republicans in voting to send the chief executive's amended bill back to committee for further study.

Mr. Robinson expressed concern about how it would affect some poorer municipalities in his district.

"Wilkinsburg, in my opinion, has been historically over-assessed," he said. "I need some assurances that the concerns of communities like Wilkinsburg are going to be addressed."

Wilkinsburg was one of five municipalities -- along with Clairton, Braddock, Homestead and North Braddock -- that would have seen reductions if Mr. Onorato had decided to use the results of the 2006 reassessment, posted by the county in March. The biggest average drop, 16.09 percent, was in Braddock.

But, countywide, residential properties would have seen an average increase of 19 percent. Unhappy with such increases, Mr. Onorato tried to put a 4 percent cap on increases, while leaving decreasing values alone.

Common Pleas Judge R. Stanton Wettick Jr. ruled that the plan was illegal because it did not assess properties uniformly.

Last month, Mr. Onorato's office said it would create new 2006 assessment values, based on adjustments to the 2002 values, using a range of factors. Yesterday, however, the chief executive scrapped that plan and said he wanted to make 2002 the base year.

After the change was introduced as an amendment at last night's council meeting, county officials acknowledged that poorer municipalities would not see the decreases that they saw under the first batch of 2006 numbers.

But county Manager Jim Flynn argued that those numbers would also end up hurting many property owners.

"I guess it's which bitter taste do you want. Do you want something you've had in your mouth for three years, the 2002 values?" he said. "Or do we want to go with something that's untested?"

Councilman Doug Price, R-Carnegie, pointed out that Mr. Onorato had described the 2002 numbers as "horrible" when he campaigned against former Chief Executive Jim Roddey.

Yet Mr. Onorato said tens of thousands of appeals after 2002 had helped correct some problems, and his base year plan would keep those new values in place.

But he also said that about 15,000 to 20,000 recent home buyers whose assessments increased after the 2002 reassessment should file new appeals.

"If they can prove that the homes on their street are much lower," Mr. Onorato said, "they can be brought back down."

Dominick Gambino, property assessment manager under Mr. Roddey, said Mr. Onorato's new plan was unfair and inappropriate. He said the numbers for that reassessment were based on sales from 1998 through mid-2001, which makes them too old to use now because the real estate market has changed substantially since then.

"I'm honored that now he has come around to think my numbers are pretty good and he wants to use them," said Mr. Gambino, who oversaw development of the 2002 numbers before Mr. Onorato replaced him. "But I'm telling him my numbers are no good any more. The market has changed since then."

Last night's council meeting led to some heated partisan exchanges, as Republicans expressed frustration with Mr. Onorato's last-minute changes and Democrats criticized Republicans for introducing their own plan only a few days ago.

"You come up here and you condemn the chief executive," Councilman C.L. Jabbour, D-West Mifflin, said in a raised voice aimed at his Republican colleagues. "He is trying to do something, but all you've done tonight is cut his legs off."

Mr. Onorato said he opposes the Republican plan, which would reuse the first set of 2006 numbers while changing the assessed value to 80 percent of market value.

Both that plan and Mr. Onorato's new base year proposal will come up Tuesday when the Special Committee on Property Assessments meets at 6 p.m. in the Allegheny County Courthouse.

Last night, council also unanimously approved a bill that would prevent the county from reaping a 5 percent revenue windfall after a reassessment, something allowed under state law. The change would not affect school districts and municipalities, who can take the windfall.