An Allegheny County judge ruled yesterday that a referendum to replace the elected sheriff with an appointed sheriff will not be on the May primary ballot.

Common Pleas Judge Eugene B. Strassburger said the county has to wait until five years after the last change in its home-rule government to try for more changes.

Allegheny County's government last changed in 2005, when voters approved an amendment to the home rule charter to replace the register of wills, prothonotary, clerk of courts and jury commissioners with one appointed director of court records and the recorder of deeds with an appointed real estate manager.

Those changes will be completed in January. Another change that made the elected coroner an appointed medical examiner has already taken place.

"Let us see what the effects are of the 2005 amendments to the home rule charter providing for appointive row offices, and after the five-year moratorium, if the County Council and county executive still desire, this referendum would be timely," Judge Strassburger wrote in his opinion supporting an injunction to stop the May referendum.

"The law on this was perfectly clear," said Thomas W. King III, one of the attorneys who challenged the referendum.

Mr. King, who represents the Sheriffs' Association of the Commonwealth of Pennsylvania, which opposed the change, said he wasn't the only person who questioned the legitimacy of the ballot question. He pointed to a memo that went out to Allegheny County Council that said the referendum might be illegal.

That memo, after citing the laws regarding the five-year moratorium, said "It thus appears that there may very well be an issue with regard to the legality of the contemplated change in the sheriff within five years of the previous row office reform amendment (which the charter itself dates as having occurred on May 17, 2005)."

During a meeting on the ballot measure in January, Councilmen Jim Burn, D-Millvale, and William E. Lestitian, D-Brookline, questioned whether the measure legally could be placed on the ballot. County Manager Jim Flynn noted that when council was considering a smoking ban, members said they didn't care if it was legal because it was the right thing to do.

Councilwoman Joan Cleary, D-Brentwood, also said the county should wait to see how the other row office consolidations work out before voting to appoint the sheriff.

"It was totally contrary to law and everyone knew it," Timothy G. Uhrich, attorney for Fred Goehringer, a taxpayer who also challenged the measure, said about the referendum. He said the attempt to put the question on the ballot was done "for a purely political reason" so that it would appear the leadership of the county was doing something to clean up the sheriff's department.

Former Sheriff Pete DeFazio and other officers were charged in a federal investigation last year into illegal political activity in the office.

County Chief Executive Dan Onorato, who proposed the legislation to appoint the sheriff, had no comment yesterday. His spokesman, Kevin Evanto, said Mr. Onorato would address the ruling at a news conference today.

Mr. Uhrich said if the county chooses to appeal the ruling, it could go to Commonwealth Court on an expedited basis so that the question could still be on the May 15 ballot.