Chicago Mayor Richard Daley has repeatedly called for stronger gun control measures, and Gov. Rod Blagojevich also got personally involved by calling lawmakers and distributing videos demonstrating the firepower of assault weapons.
The National Rifle Association argued the proposed ban was too broad.
The measure was an amendment Rep. Edward Acevedo attempted to add to an existing bill. It failed on a vote of 57 to 58 in the House.
A swing of one vote would have given the amendment enough support to be added; approving the bill would then have taken 60 votes.