OLYMPIA — After weeks of waiting, state lawmakers on Thursday finally got to see the details of a $300 million tax package that the Sonics are proposing for a new arena in King County.

The legislation, which probably won't be formally introduced until Monday, is similar to what the team's previous owners failed to sell to the Legislature the past two years. It would allow King County to extend several existing taxes that are currently being used to pay off the debt on Safeco Field, Qwest Field and the Kingdome, which was demolished in 2000.

"These are the same taxes we've been paying all along," said Sen. Margarita Prentice, D-Renton, the Sonics' biggest supporter in Olympia.

So far, however, support in the Legislature is spotty at best.

"I know there are some senators interested," said Senate Majority Leader Lisa Brown, D-Spokane, "but I just don't know how that translates yet into broader support."

Aside from paying for a new arena for the Sonics and Storm basketball teams, the tax package proposed in Senate Bill 5986 would raise an additional $123 million that King County could use for other purposes. The bill says the top-priority use for the money is arts and cultural activities, followed by maintenance on existing sports facilities.

Sonics lobbyists worked the halls Thursday, rounding up sponsors for the draft legislation. By the end of the day, five senators had signed onto the bill. The team plans to start looking for sponsors in the House next week.

Prentice, who chairs the powerful Senate Ways and Means Committee, will hold a hearing on the bill Tuesday.

She said she assumed Sonics owner Clay Bennett would be ready to announce an arena site by then, but team officials weren't making any promises.

"I can't predict that," said team spokesman Jim Kneeland. "We're working as quickly as we can to get the site."

The team is deciding between sites in Bellevue and Renton. Kneeland said the team had hoped to have that finalized before formally proposing the tax package.

"It just didn't make sense to wait any longer; we had to get it moving," he said.

Sonics consultants met with Bellevue city officials Thursday and asked what the city was prepared to offer for a new arena. City officials did not have an answer because they said they still needed more information, such as how much money the building would make, said City Manager Steve Sarkozy.

"We're still in the information-gathering mode," Sarkozy said. "We're trying to understand their business plan, their revenue structure and where they see gaps in their financing."

Renton city officials have not met with the team in person but have spoken on the phone, said Alex Pietsch, city economic-development director. The team has not directly asked city officials what they would offer, though both parties have discussed parking and other improvements at an arena site.

Pietsch said team officials assured him they don't need any more information from the city to make their decision. "I feel like we've done what we can."

If the team chooses Renton, "we'll really be able to dive in and really understand what the economics are," he said.

The new arena — a multipurpose facility that could accommodate other professional sports, such as hockey — is expected to cost more than $500 million. The team and other private-sector sources would pick up the portion not covered by taxpayers.

Seattle Times reporters Keith Ervin and Andrew Garber contributed

to this report.

Ralph Thomas: 360-943-9882 or rthomas@seattletimes.com