SPRINGFIELD, Ill. — In a vote that stunned most legislative leaders, House members soundly defeated a tax incentive plan last week designed to keep the state’s two largest financial exchanges from moving out of Illinois.

While the Illinois Senate passed the bill by a veto-proof majority, the Illinois House barely found members who would support it, voting against the measure 99-8.

Democrats led both chambers in Illinois; while the Senate had bipartisan support, House Minority Leader Tom Cross (R-Plainfield) said he wouldn’t back the measure if it included an expansion of the state’s earned income tax credit. That is one element of the plan Gov. Pat Quinn said must be in the legislation for him to sign it.

Rep. John Bradley (Marion), head of the House’s Revenue Committee and the Democrats’ lead negotiator, said he was surprised at the outcome. But, he also said he will work to find a way to have a revised measure introduced for a vote before the end of the year. “There’s no other way to do this but to figure out some way to get bipartisan support on this,” Bradley said. “We had it, and part of this process is determining how we lost it.”

The tax incentive package would cost the state an estimated $325 million a year, with the CME Group, Inc., the Chicago Board Options Exchange (CBOE) and Sears Holding Corp. receiving about one-third of that in corporate income tax breaks.

CME and CBOE have been pushing for tax relief all year, stating most of their business doesn’t occur on trading floors within the state but electronically, with trades originating out of state. Therefore, executives with the companies argued, CME and CBOE shouldn’t continue to pay corporate income taxes on all transactions.

Most lawmakers seemed to agree, and then as negotiations continued in drafting a bill, more elements were added. An extension of a research and development tax credit critical to Caterpillar was included; Quinn insisted on adding the earned income tax credit for low-income residents; and Sears said if it didn’t received some type of break, it would consider moving its headquarters out of suburban Chicago.

Fueling the requests was the state’s early 2011 increase in its corporate income tax from 4.8 to 7 percent.

Bradley said he’s hopeful most of the elements of the latest version of the tax package will pass because it is critical for the state not to lose corporate giants such as CME and Sears. He has been meeting with Cross and talking with other legislative leaders throughout the weekend. Chicago Mayor Rahm Emanuel also has been in on the negotiations.

For Cross, finding a way to cover the additional cost of expanding the earned income tax credit is critical.

“We’ll continue to offer alternatives and see if we can find middle ground, but we’re pretty firm on the position that we don’t have any extra money (to expand the earned income tax credit),” he said.

Meanwhile, CME officials met with Indianapolis Mayor Greg Ballard on Friday. Indiana is one of several states hoping to convince CME to move. “We have a very competitive offer and we’re excited and happy to be talking to CME officials,” Ballard told The Wall Street Journal after the meeting.