Also to the dismay of Republican lawmakers, the House adjourned Monday night without even taking up the question of a special election, ending that prospect at least for now.

State Representative Tom Cross, the Republican leader, had urged his colleagues to pass legislation setting a primary election in February and a general election in April to fill the Senate seat. Republicans said they suspected Democrats were stalling on the proposal, perhaps all the way until impeachment proceedings are concluded, to allow Mr. Quinn to become governor and make the appointment.

Surprising many, Mr. Blagojevich has left open the possibility that he would sign a bill allowing a special election, which would take away his power to choose Mr. Obama’s successor. “That’s something that he’s been a supporter of, letting people decide who their elected officials are,” Mr. Guerrero said. “He just has to see the legislation.”

Even as members for the impeachment committee were being named, it was clear that few here understood precisely how the impeachment process would go forward. There is little recent precedent for it, aside from a 1997 effort to impeach James Heiple, an Illinois Supreme Court chief justice. That case ended without a final decision by lawmakers because Mr. Heiple decided not to run for re-election.

And the standards and procedures for impeachment, described in the state Constitution, are extremely broad, offering scarce guidance other than calling for a majority vote in the House, a trial in the Senate presided over by the State Supreme Court’s chief justice and, for a conviction, a two-thirds majority vote in the Senate.

“They’ll have to decide what their standard is,” said Dawn Clark Netsch, a political scientist at Northwestern University who was once a Democratic lawmaker and comptroller of Illinois. “They’re going to look to language or grounds or standards used in other states. They may be somewhat influenced by language in the U.S. Constitution, but they certainly aren’t bound by any of that.”

Some experts said the impeachment inquiry might also create problems for federal prosecutors’ criminal proceedings against Mr. Blagojevich, if witnesses are compelled to testify and are granted immunity.