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WASHINGTON — Rep. Rahm Emanuel (D-Ill.), incoming chief of staff to President-elect Barack Obama, will formally resign his House seat Friday.

The timing of the announcement has been a subject of speculation for weeks as controversy over Obama’s vacant Senate seat has swirled. On Monday, Emanuel sent a letter to embattled Illinois Gov. Rod Blagojevich saying he would leave his congressional seat at the end of the week. Blagojevich held the seat, representing Chicago’s North Side, before he was elected governor in 2002.

Blagojevich is accused by federal prosecutors of attempting to leverage his power to appoint Obama’s successor in the Senate for personal gain. The governor has no authority in replacing members of the House.

Instead, once Emanuel formally resigns, Blagojevich will have five days to set a date for a special election. That election must be held within 115 days. Emanuel has represented Illinois’ 5th Congressional District for almost six years.

Emanuel’s contacts with Blagojevich’s office concerning the Senate vacancy and his own replacement have been closely scrutinized.

Last week, Obama’s transition office released the findings of an internal review that said Emanuel had “one or two” conversations with Blagojevich concerning his House seat and possible successors to Obama. He also had several conversations with Blagojevich’s then-chief of staff, John Harris, the report said.

The report concluded that Emanuel did not discuss giving Blagojevich a position in Obama’s Cabinet, a private-sector job “or any other personal benefit for the governor.” The Illinois House committee investigating impeaching Blagojevich said Saturday that it would not compel Emanuel to testify about his contacts with the governor, citing a plea from U.S. Atty. Patrick Fitzgerald, who feared it would impede his investigation of Blagojevich.

Emanuel came to prominence as an adviser to President Bill Clinton.

His departure from the House will leave a void in the Democratic leadership on the Hill. Widely credited for the Democratic Party’s big gains in the 2006 midterm elections, Emanuel, 49, has been viewed by some as a future speaker of the House. There has been speculation that he might seek to return to his 5th District seat for the 2010 election in order to return to that track.

Whether any option to reclaim the seat will exist for Emanuel will depend, of course, on who assumes it. Chicago-area politicians who could seek the office include Aldermen Thomas Allen and Gene Schulter, Cook County Commissioner Mike Quigley, state Reps. John Fritchey and Sara Feigenholtz and former Rep. Nancy Kaszak. According to the Illinois Board of Elections, Blagojevich is not required to set a date for a party primary before the special election, but can.

Emanuel’s letter to Blagojevich was surprisingly personal for someone whose future boss—Obama—has called for the governor’s resignation. But the two have known each other for years, with some even labeling Emanuel as a mentor to Blagojevich.

“As sons of immigrants to this country,” Emanuel wrote, “you and I have a deep appreciation for the opportunities America provides to those who are willing to work hard and sacrifice for their children.”

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