"We anticipate that a large number of these documents would be exempt in whole or in part,'' the city said in one of several responses. "Assuming that the review was done by an assistant corporation counsel being paid $60,000 per year, the cost of this review would be approximately $50,000."

The Tribune then asked instead for a log of the emails — in essence a snapshot of the inboxes for the mayor and his aides — so that they could be used to narrow the request to email correspondence that might be of public interest. The administration denied that request as well, saying the subject lines might also contain information the city is not required to disclose.

Finally, last week the Emanuel administration said it could not disclose a complete email log even without the subject line. According to Emanuel spokeswoman Jenny Hoyle, 90 percent of the emails have been deleted by Emanuel and his top aides, and a log is no longer available.

The city provided a log of the other 10 percent — roughly 2,800 emails — that showed the time, date, sender and recipient. But the city removed the subject line.

The main reason Emanuel spokespeople cited for denying access to emails was an exemption in state law for "preliminary draft" material, which allows public officials to withhold forever any discussions, opinions or discourse that precede a final decision on how to spend tax dollars.

"By way of example, a subject line could be 'proposed change to City ordinance to reduce maximum allowed building height,'" Emanuel spokeswoman Jenny Hoyle wrote in one of several responses to the Tribune. "In such cases, even the subject line would be pre-decisional in nature."

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The administration provided cellphone records that did not include a single telephone number for either incoming or outgoing calls, making it impossible to discern how the phones might be used to conduct city business. The city said it would be "extremely burdensome" to determine which numbers were public under the law and which were not.

Emanuel doesn't have a city-issued phone and uses an aide's phone to make city-related calls, Hoyle said. The Tribune requested the records for that phone, among others.

Ann Spillane, chief of staff to Attorney General Lisa Madigan, whose office works to resolve public records disputes, said cellphone bills are public, as well as email strings.

"I don't know anything about the records retention policy at the city of Chicago," she said. "But they cannot simply by virtue of the way they handle public records, make a claim that it is unduly burdensome to provide them."

The attorney general last month also ruled in a similar case that publicly funded cellphone records must be disclosed, telling Franklin Park officials they could not justify their claim that providing five months of cellphone bills for four village officials was unduly burdensome.

Emanuel's communications director issued a statement saying the Tribune's request for the emails and other communications from the mayor's office was unreasonable.

"The Chicago Tribune declined to narrow the request sufficiently enough to provide the information in the required 10 days," Mather said in an email. "The city of Chicago responds to more than 40,000 (Freedom of Information Act) requests each year, and we are committed to fulfilling all requests that do not place an undue burden on taxpayers."

But the mayor's office likewise rejected more specific requests for records pertaining to his major proposals.

The newspaper sought the emails, memos and studies behind the administration's recently announced plans to increase water and sewer rates for homeowners and raise many vehicle sticker prices. After two weeks of extensions, the mayor's office denied those requests as too broad, asking the newspaper to identify which officials were involved. Negotiations continue.

The Tribune also asked the Chicago Police Department for detailed crime statistics going back to 2006 and a list of police officers investigated by the department.

The department also used the "unduly burdensome" exemption to deny the newspaper's request for a log of closed internal affairs case files, saying it would be too much work to notify each officer, as is required under the city's contract with the police union.

Chicago Police Superintendent Garry McCarthy did not respond to interview requests on the matter.

The Emanuel administration last month released a district-by-district accounting of police staffing levels following a yearlong legal battle with the Tribune. It argued the records containing the information were secret on grounds that public disclosure of how many police work in each district would make neighborhoods less safe.

The attorney general's office disagreed, as did a Cook County judge who ruled the Police Department must release the records.

"These are public documents under the Illinois Freedom of Information Act, and our requests for them are legitimate," Tribune Editor Gerould Kern said. "As citizens, we are entitled to know how our government works."

The Tribune has reported that government officials routinely deny access to public records based on a series of gaping and often-abused exemptions to the open records law. That has continued even under revisions adopted in 2009 following the corruption arrests of two successive governors.

The Tribune survey found such requests are less burdensome for many other major cities.

In Phoenix, all emails to and from the mayor and City Council are automatically directed to the city clerk's office, where they are viewable on a public computer terminal.

In Seattle, the details of every closed police internal affairs case are posted online. In Hartford, all the numbers on the mayor's cellphone bill are of public record.

In Boston, city officials in 2009 posted online some 11,000 emails from a city official following a Boston Globe public records request that revealed the official had been deleting his emails against state records laws.

dkidwell@tribune.com