State Rep. Julie Hamos will be the third major Democrat to announce her candidacy for Rep. Mark Kirk’s (R) soon-to-be-open seat.

Hamos will announce her candidacy for the suburban Chicago seat today with several state lawmakers by her side. The 2006 and 2008 nominee, marketing consultant Dan Seals, and state Sen. Michael Bond have already announced their campaigns for the Democratic nomination.

Kirk’s retirement to run for Senate next year leaves his district wide open in 2010 and sets up a prime pickup opportunity for Democrats, who have spent millions of dollars in the past two cycles targeting Kirk’s seat.

Launching Senate Bid, Giannoulias Hits Kirk

State Treasurer Alexi Giannoulias (D) officially became a candidate for Senate over the weekend. He announced Sunday that he was moving his campaign out of the exploratory phase to run for President Barack Obama’s former seat.

In his announcement, Giannoulias frequently referred to Obama and called him his “friend and mentor— in a written announcement to supporters — although Obama has not endorsed Giannoulias. Giannoulias also took a shot at the likely GOP nominee, Rep. Mark Kirk, in his announcement.

“This race will offer voters a stark choice between the failed past or a promising future — a clear choice between the right course and the wrong one,— Giannoulias said.

Giannoulias, however, is not expected to be the only Democrat to run for the seat that appointed Sen. Roland Burris (D) will retire from in 2010. Chicago Urban League President Cheryle Jackson has opened an exploratory bid. Businessman Chris Kennedy (D) was close to announcing his own bid for the Senate seat, but the Chicago Sun-Times recently reported he was interested in running for governor.

In related news, another Republican, former Harvey Alderman John Arrington, announced he will run against Kirk in the GOP primary.