CHICAGO (AP) – Senators Barack Obama and John McCain lead by better than 2-to-1 among likely Illinois presidential primary voters, according to a poll released Saturday.

But 20 percent of Democrats and 17 percent of Republicans are still undecided heading into Super Tuesday, and nearly a quarter of the Democrats and a third of Republicans who had made a choice said they still might change their minds.

Obama, a longtime Chicagoan, led among Democrats with 55 percent. New York Sen. Hillary Rodham Clinton, who was born in Chicago and raised in suburban Park Ridge, has support from 24 percent.

Among Republicans, Arizona Sen. McCain found support from 43 percent of likely GOP voters, compared with 20 percent for former Massachusetts Gov. Mitt Romney, 15 percent for former Arkansas Gov. Mike Huckabee and four percent for Texas Rep. Ron Paul.

The poll, conducted for the Chicago Tribune and WGN-TV by Market Shares, has a margin of error of plus or minus 4.4 percentage points. The survey of 500 Republicans and Democrats was conducted Tuesday through Thursday.

Forty-eight percent of Democrats said Obama has the best chance of beating a Republican in November, compared to 23 who favored Clinton. On the Republican side, 56 percent said McCain has the best chance of winning in November, compared with 16 percent for Romney and four percent for Huckabee.

Both Democrats, with 62 percent, and Republicans, at 55 percent, cited the economy and its impact on employment as their top concern. Democrats listed health care and the Iraq war as second and third among their concerns, while Republicans cited illegal immigration and the war in Iraq.

Meanwhile, a separate Tribune/WGN-TV survey found that none of the Democratic candidates for Cook County state’s attorney can claim a solid majority of support among likely voters.

Forty-four percent of the 404 likely voters surveyed said they were undecided in the race to replace State’s Attorney Dick Devine.

Cook County Commissioner Larry Suffredin had 17 percent, Chicago Aldermen Tom Allen and Howard Brookins each had 11 percent, as did Cook County prosecutor Anita Alvarez.

Robert Milan, Devine’s top assistant, had 3 percent and Tommy Brewer, a defense lawyer and former FBI agent, had 2 percent.

The poll had a margin of error of plus or minus 5 percentage points.