Updated: April 22, 2014 10:10PM

Before a standing-room-only crowd of immigration reform activists, Republican U.S. Senate hopeful Jim Oberweis on Tuesday offered a mea culpa for a track record of taking harsh stances on illegal immigrants.

Speaking at the Illinois Business Immigration Coalition alongside a Mount Rushmore of Illinois Republicans, Oberweis admitted he was known as a “hawk” on immigration reform but said he has evolved on the issue over the last decade.

Oberweis was among a slew of GOP political heavyweights attending the event aimed at urging Illinois’ U.S. House delegation to vote on a measure to reform immigration. Former Gov. Jim Edgar, former U.S. House Speaker Denny Hastert and Republican gubernatorial candidate Bruce Rauner also spoke at the event at the Chicago Club, 81 E. Van Buren.

However, neither Oberweis nor Rauner would embrace Senate-backed comprehensive legislation awaiting a response in the House. Republican House leaders similarly have shown no interest in backing the Senate plan, saying they would prefer a piecemeal approach that begins with reinforcing border security.

As he moves into the general election campaign against U.S. Sen. Dick Durbin, D-Chicago, Oberweis, a state senator from Sugar Grove, is trying to tackle head-on what may be his biggest weakness: a controversial TV ad Oberweis ran in 2004. The spot featured Oberweis in a helicopter hovering over Soldier Field, warning that there were enough illegal immigrants to fill that stadium.

Durbin’s campaign on Tuesday called the spot the “most inflammatory and divisive campaign ads in Illinois history.” Yet, Oberweis’ mere invitation to the reform event is evidence he is viewed as having moderated on the issue.

Introducing Oberweis, Joshua Hoyt, co-chair of the Illinois Business Immigration Coalition, said over the years “there were few more bitter adversaries” to immigration rights groups than Oberweis. “For years Senator Oberweis has been an immigration hawk,” Hoyt said. “But he joins the Illinois Business Immigration Coalition today in the spirit of reaching across difference to find workable bipartisan solutions.”

Oberweis said he still supports greater emphasis on border security paired with other reforms, including allowing children of illegal immigrants brought to this country to obtain citizenship.

“Early on, I spoke up forcibly on the need to secure our borders and bring immigration into this country under the rule of law,” Oberweis said. “I regret the harsh tone of my rhetoric 10 years ago. But my principles remain intact.”

After his prepared remarks, Oberweis was asked about that ad and how it’s bound to haunt him during his campaign against Durbin. “It was a mistake,” Oberweis told reporters after his prepared remarks. “I wish that I hadn’t [done the ad], yes . . . it was poorly done.”

Email: nkorecki@suntimes.com

Twitter: @natashakorecki