SEATTLE -- Attempts to build a nearly $500 million arena that could bring the NBA back to Seattle took another step forward on Wednesday.

And if an NHL team turns out to not be part of the equation, the public investment will be less than originally believed.

The city, King County and private investor Chris Hansen announced a memorandum of understanding on Wednesday laying out the financial responsibilities for the proposed venue.

The proposal included two significant changes, the result of three months of negotiations between Hansen and the local municipalities, from the original unveiled in February. The agreement indicates that construction on the facility could begin with only an NBA franchise on board. Previously, it was believed that both an NBA and an NHL franchise would need to be committed tenants to make the plan work.

The plan calls for nearly $300 million in private investment from Hansen's group. The amount of public support would be capped at $120 million if it's only the NBA making a return to the Puget Sound region. It would be $200 million if NBA and NHL franchises are involved.

The goal is still to bring both professional leagues, but the project can move forward with only the NBA in hand, which is the focus of Hansen, a San Francisco hedge-fund manager and main investor in the project.

"Our job is, as soon as possible, when we have an agreement in place, we'll be very aggressive in our efforts to make sure that everybody knows that we would like to have a franchise back here," Hansen said. "I don't want to comment on specific franchises again, but we'll do the best that we can."

The agreement now goes before the Seattle City Council and King County Council for review. Both entities would need to approve the agreement for the project to move forward. No construction would begin until after a franchise has been acquired.

Other little nuggets are laid out within the 24-page MOU, including the bullet point that any NBA team using the facility will have to be named the SuperSonics, subject to NBA approval. Hansen also included a side letter where he suggests that KeyArena would be used for up to two years as a temporary home with a handful of upgrades paid for by Hansen's investor group, ArenaCo. Following its use as a temporary facility, Hansen suggests KeyArena could become a smaller arena, a theater venue or exhibition center.

But the bulk of the MOU focused on the financial details of the public investment, which is to be paid for through taxes and revenues generated by the new arena and has a number of public protections included.

The project calls for about $290 million in private investment from Hansen's group, along with $200 million from the city and county through 30-year bonds. Any franchise that comes to Seattle and uses the arena would be required to sign a non-relocation agreement that would span the life of those bonds.

All construction costs, including overruns, would be paid for by Hansen's group, along with all environmental studies and permitting. Once that process is completed, most of the public investment is placed on the city.

The MOU calls for an initial investment of $100 million by the city for acquisition of the project site. During a second investment window, the city would contribute another $20 million if both an NBA and NHL team are acquired, with the remaining $80 million in public investment being bonded by the county.

If only an NBA team is acquired, the public bonding would be capped at $120 million with $115 million coming from the city and only $5 million coming from the county.

"We have to keep taking steps along the way," Seattle mayor Mike McGinn said. "I guess what I'm trying to say is it would be a real shot in the arm to our community to bring back the Sonics and that has value."

Specifications for the arena were also released. It would hold up to 19,000 for concerts, 18,500 for basketball and 17,500 for hockey and be constructed on a site just south of downtown Seattle in the neighborhood including Safeco Field and CenturyLink Field.

Putting a third sports venue is the same area has drawn concern about traffic and transportation, most notably by the Port of Seattle and the Seattle Mariners. Hansen's group has paid for a traffic study currently being conducted by the Seattle Department of Transportation.