The chief of staff to Illinois Gov. Rod Blagojevich, D, resigned Friday after wiretapped conversations revealed his role in what prosecutors describe as a sweeping 'pay-to-play' scandal, a case that has grown more complicated and legally controversial since the two men were arrested before sunrise Tuesday.

WASHINGTON — The chief of staff to Illinois Gov. Rod Blagojevich, D, resigned Friday after wiretapped conversations revealed his role in what prosecutors describe as a sweeping "pay-to-play" scandal, a case that has grown more complicated and legally controversial since the two men were arrested before sunrise Tuesday.

John Harris's resignation came as pressure intensified for Blagojevich to step down and for President-elect Barack Obama's transition team to disclose details of its contacts with the governor's office about the selection of a successor to Obama in the Senate. Blagojevich and Harris are accused of planning to sell the vacant seat to the highest bidder, discussing the terms in blunt language with several possible contenders or their emissaries.

Harris played a central role in wiretapped conversations in which the two discussed the scheme, according to court papers. And while a criminal complaint against the men appeared to offer damning confirmation of improper discussions, debate raged within the legal community about whether U.S. Attorney Patrick Fitzgerald moved prematurely to bring bribery and conspiracy charges before the consummation of an illegal act.

Fitzgerald has said he acted quickly because he feared that Blagojevich, who has sole power to make the Senate appointment, would carry out some of the illegal schemes discussed on the tapes, including killing funding for a children's hospital project to strong-arm contributions from a reluctant hospital executive.

The case has enmeshed Rep. Jesse Jackson Jr., D-Ill., who has been identified as the complaint's "Senate Candidate 5" but who has said he is "not a target" of the criminal probe. Representatives for Blagojevich did not comment on a report in the Chicago Tribune that businessmen with ties to him and Jackson held a fundraiser last weekend, followed two days later by a meeting between the governor and Jackson to discuss the Senate seat.

Late Friday, people close to Rahm Emanuel, the incoming White House chief of staff and House member who succeeded Blagojevich in the 5th District seat, said he also is not a target of the probe. Blagojevich told Harris in one Nov. 13 recording that he wanted to be able to call a "president-elect advisor," according to the complaint, and ask, "Can you guys help ... raise 10, 15 million?"

Among those who have confirmed recent contact from the FBI are Tom Balanoff, a Democratic Party loyalist who leads the Illinois chapter of the Service Employees International Union, and officials at the Chicago Tribune. Recordings captured Harris musing about a deal in which the SEIU would find Blagojevich a high-paying job with an affiliate. Tribune officials had been pressured to fire editorial writers critical of the governor, in exchange for state help on the sale of the company's Wrigley Field baseball park, the complaint said.

Still unknown is whether anybody in the Obama camp knew of the extent of the allegations against the governor and whether they shared concerns with law enforcement. Obama denied Wednesday that any of his staff members engaged in horse trading over the Senate seat.

The resignation of Harris was seen as a possible first sign that he might be cooperating with federal investigators. His lawyer Jim Sotos said Friday that "John resigned because he believed it was the right thing to do," but he declined to comment further.

Word of the resignation came as Illinois Attorney General Lisa Madigan, D, took the unprecedented step of petitioning the state's highest court to seek Blagojevich's ouster.

Federal prosecutors and FBI agents have mined public corruption in Illinois for more than five years, slowly building a case that they called Operation Board Games. Prosecutors secured convictions against insiders who did not bend, including Antoin "Tony" Rezko, once an adviser to Blagojevich and a fundraiser for both the governor and Obama. Rezko, whose criminal case gained wide attention during Obama's Democratic primary campaign, is now helping the government in exchange for a reduced prison sentence.

Legal experts said the strength of any prosecution may rise or fall on recordings that federal prosecutors made starting in late October, when they won permission from a federal judge to wiretap the governor's campaign office and his home telephone line. Law enforcement officials said this week that they have not released all of the taped evidence.

Blagojevich told four Chicago ministers who prayed with him Friday that he is not guilty. "It's a witch hunt, that's what it is," said the Rev. Leonard Barr, associate minister of the Fellowship Missionary Baptist Church. "They haven't come up with anything impeachable that I can see, other than a lot of innuendo and a lot of rumors, and conversation they got through electronic surveillance."

But Joseph di Genova, a former U.S. attorney in Washington, on Friday raised the possibility that investigators are enjoying the fruits of wiretaps that they have not disclosed to the defendants or the public.

"He's holding on to the governorship because that's the only leverage he has," di Genova said.

Former prosecutors said Blagojevich's wife, Patricia, who was overheard making profane suggestions about the Tribune on some recordings, also may face criminal investigation, heightening pressure on her husband.

Andrew Lourie, former chief of the public corruption unit at the Justice Department, emphasized that prosecutors must build a case on more than just statements.

"If you're not actually agreeing to do something illegal and taking one step to violate the law, then it's not a conspiracy," he said.

Witnesses, documents or bank records can help prove that link, Lourie added. One reason the Blagojevich investigation may have taken so long is the challenge in making that connection, other legal experts said.

Fundraising and campaign-donation cases can present challenges, since the expectation of a favor is not enough to meet high legal burdens.

"Perhaps the distinction rests on the fact that Governor Blagojevich was so foolish as to explicitly demand contributions in return for official actions, whereas most politicians are smart enough to leave such matters unstated," said Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington.

In other corruption probes, authorities have presented as evidence long lists of things that lawmakers received. In the case against former congressman Robert Ney, R-Ohio, for instance, prosecutors noted numerous gifts from lobbyists, including a Scotland golfing vacation, poker chips and gourmet meals. Ney pleaded guilty.

Such connections are less clear in the Blagojevich case.

— Staff writers Peter Slevin in Chicago and Anne E. Kornblut in Washington contributed to this report.