More than 500 people, many of them supporters of a proposal to bring the Sonics back to Seattle and build a new sports arena in the Sodo neighborhood, overflowed two City Hall meeting rooms Thursday night with testimonials about what the return of professional basketball would mean to them and the city.

Some Port of Seattle and labor leaders spoke against the proposal, saying it would jeopardize freight mobility from the container terminals on Elliott Bay and risk family-wage jobs.

But others told the joint meeting of the Seattle and King County councils that the elected officials should craft a "win-win" solution that protects the maritime industry while also bringing a state-of-the-art sports and entertainment venue to the city.

"You guys have been handed a golden ticket," said Kyle Anderson, who like many of the scores of speakers, identified himself as a lifelong Sonics fan.

"All the positives of this outweigh the negatives. I really hope we do this."

Metropolitan King County Council Chairman Larry Gossett called the joint meeting "historic" and said it was one of the few times in the past 40 years that the two bodies had jointly met.

The two councils are poised to vote in August on a proposal by San Francisco investor and Seattle native Chris Hansen to build a $490 million arena with $200 million in public funding.

Both councils have been holding hearings and seeking expert opinion on the economic benefits and risks to the deal since an agreement was reached in May between Mayor Mike McGinn, County Executive Dow Constantine and Hansen.

"In all of our major public-policy issues, whether we are establishing new programs or cutting existing ones, public input has ended up making a huge difference. Your testimony tonight can have a very significant impact on your elected leaders," Gossett at the start of the hearing.

Port of Seattle CEO Tay Yoshitani urged the councils to do environmental study, including consideration of alternate sites, before approving the arena deal.

"We know the arena could seriously affect our cargo operations now and in the future. It could affect the grid of streets in Sodo that are now already congested," he said.

Peter Goldman, an environmental attorney, also told the councils that approving the proposal before an in-depth environmental review is completed would be contrary to state law and good public policy.

Earlier in the day, in a live online chat at The Seattle Times, Hansen said his investment group was committed to addressing the traffic impacts in Sodo, "but we don't want to be the only ones on the hook for all of the issues that are being brought up."

More than a dozen members of the union representing stagehand workers at KeyArena asked the councils to preserve their jobs, which they said provide good pay and affordable health care. They asked that any arena deal provide for the continued operation of KeyArena and not privatize their work. The city operates KeyArena.

Despite the remarks urging caution, the evening belonged largely to Sonics fans.

In a message on his website, sonicsarena.com, Hansen asked fans to turn out, but "handle ourselves with class" by listening respectfully to the opposition and not booing or hissing.

The fans responded, sitting politely through the opposing testimony, while applauding, sometimes raucously, as men and women, young people and old, told the councils what a good deal Hansen was offering and how much the Sonics, who were moved to Oklahoma City and renamed the Thunder in 2008, had meant to them.

They applauded loudly when restaurateur Mick McHugh announced he was delivering 12,600 signatures in support of the arena proposal.

Joel Craig, business agent for Local 7 of the International Association of Heat and Frost Insulators and Allied Workers, called the number of fellow laborers out of work during the economic downturn "tragic."

"I never thought I'd see the return of the Sonics in my life. This is a large city. This is a progressive city. Spend some money and put people back to work," he said.

Ryan Karpenko told the councils that the best gift he had ever received was a special-order Sonics jersey when he was 9 years old.

The next week, he said, his father took him to a basketball game. He wrote a thank-you letter to his dad, he said, which still hangs in his parents' bedroom.

"One thing statistics can't account for, that's love," Karpenko said. "I loved the Sonics and the Sonics loved me back. A lot of people in this room feel the same way."

Lynn Thompson: 206-464-8305 or lthompson@seattletimes.com. On Twitter @lthompsontimes.