It’s looking increasingly likely that state Treasurer Alexi Giannoulias will be Democrats’ anointed candidate in the 2010 Illinois Senate race.

Giannoulias’ aides confirmed a local report that the powerful state chapter of the Service Employees International Union will endorse Giannoulias — a sign that he will be national and local Democrats’ pick to face Rep. Mark Kirk (R-Ill.) in the general election.

Giannoulias, who announced his candidacy early this year and was the first Democrat to get in the race, took somewhat of a backseat while national Democrats openly courted other candidates to run. State Attorney General Lisa Madigan (D) turned down overtures from the White House to run for the seat formerly held by President Barack Obama. Meanwhile, those familiar with businessman Chris Kennedy (D), who had been widely expected to enter the race, say his campaign has gone silent in recent weeks.

The window of opportunity for other candidates to get into the race continues to close as petitions to get on the ballot started circulating last week.

Chicago Urban League President Cheryle Jackson (D) announced this week that she is running, but local operatives say she will have trouble overcoming Giannoulias’ head start. And now that the young state treasurer has picked up the backing of the most prominent union in Democratic politics, it will be even more difficult for Jackson to catch up in the less than six months before the Feb. 2 primary.

The SEIU and other labor groups have often stayed out of Democratic primaries in Illinois with some notable exceptions.

Organized labor split in the 2004 open-seat race, when the SEIU backed Obama and the AFL-CIO supported state Comptroller Dan Hynes in the crowded Democratic primary. The SEIU also waded into the 2002 Democratic gubernatorial primary when it endorsed now-disgraced former Gov. Rod Blagojevich over Roland Burris in a three-way contest.

One Democratic activist who has worked in the state said that the SEIU is most powerful and useful for campaigns in Chicago — where the super-majority of Democratic primary voters reside. But the Democratic activist also pointed out that even the SEIU’s reputation was hurt by the Blagojevich scandal because they supported him in the 2002 gubernatorial primary.

“They’ve been definitely tainted by the Blagojevich scandal,— said the operative. “They came out strongly for him in the 2002 primary.—

Another Democrat who worked on the Blagojevich campaign in 2002 said that he did not think the SEIU’s backing boosted the campaign much, except for turning out a large crowd at the initial campaign announcement.

“They brought out bodies, but you couldn’t really count on the level of work with these guys,— said the former Blagojevich aide.

With Kennedy off the radar in recent weeks, the SEIU had little other option for where they could throw their support.

At least two well-placed sources who were working with Kennedy on his potential bid said they have been out of communication with him for several weeks and they do not expect him to run for office. What’s more, several Illinois Democrats said they had heard nothing from Kennedy or his associates in recent weeks.

The Chicago Sun-Times reported that Kennedy also recently suffered four broken ribs during a recent water skiing accident in Hyannis Port, Mass. Kennedy’s aunt, Eunice Kennedy Shriver, also passed away this week.

This isn’t the first time that Kennedy has openly considered a race for federal office then ended up not pulling the trigger on a campaign. He also considered running for Kirk’s House seat, as well as this Senate seat in 2004.