By Renita Young

CHICAGO (Reuters) - Gun control supporter Robin Kelly won the Democratic primary for a Chicago area U.S. House seat on Tuesday, propelled by more than $2 million in television ads highlighting the guns issue bankrolled by New York Mayor Michael Bloomberg.

Kelly, a former Illinois state representative, said in her victory speech that the vote was a setback for the powerful gun rights lobby, the National Rifle Association.

"The voters sent a message that tells the NRA that their days of holding our country hostage are coming to an end. And their days of scaring Congress into submission on gun control are coming to a close," Kelly said to cheers from supporters.

The NRA fiercely defends the Second Amendment to the U.S. Constitution setting out the right to bear arms.

The Chicago special election was the first U.S. electoral test since gun control rose to the top of the political agenda after a gunman killed 26 people at an elementary school in Newtown, Connecticut, in December.

Since that massacre, which took the lives of 20 school children, President Barack Obama has pushed Congress to pass tighter gun restrictions and Bloomberg has vowed to use some of his fortune to help battle the political influence of the NRA.

The special election was to fill the seat of indicted former U.S. Representative Jesse Jackson Jr, who resigned in November citing health problems and pleaded guilty in federal court last week to using campaign funds for personal enrichment.

Jackson was a reliable vote in Congress for gun control. Until Bloomberg elbowed into the race, polls had shown that the special election might be won by Debbie Halvorson, a former congresswoman who had an A+ rating from the NRA and opposed an assault weapons ban.

Bloomberg blanketed Chicago television with ads on the gun issue, attacking Halvorson and endorsing Kelly in the final days of the campaign.

"He turned this election into a referendum on the NRA," said Chicago Democratic political analyst Don Rose.

A little over an hour after the polls closed, Halvorson called Kelly to concede defeat, saying that Bloomberg's television ads had overwhelmed her campaign.

"There was $2.3 million minimum spent against me," Halvorson told supporters. "That's the way it is. I can't help it."

The Illinois affiliate of the NRA had asked its members to vote for Halvorson. Continued...