The St. Paul City Council, the city’s Port Authority and the Metropolitan Council agreed Wednesday to fashion a long-term lease aimed at landing a privately built big league soccer stadium on a publicly held Midway site once used to store buses.

Although the Port Authority (acting as the city’s agent) and the Met Council already have had informal talks, Wednesday’s joint powers agreement puts an official sheen on negotiations and sends a clear message to team owners and Major League Soccer that St. Paul is serious about becoming the home for a new Minnesota franchise.

Successful lease negotiations would give the city site control should Major League Soccer officials approve the St. Paul location, at Snelling Avenue and Interstate 94, for an 18,500-seat stadium. The league may not make its decision for several months.

The facility would house Minnesota United FC, a team owned by Bill McGuire and investors including the Pohlad family and Star Tribune owner Glen Taylor.

The plan is that the city — or possibly a stadium authority — would lease the site from the Met Council, which would continue to own the land and use lease payments to develop transit-related amenities on the site. The team would deed the stadium to the city once it’s built and reimburse the city for lease payments.

City ownership would ensure that the property is tax-exempt, a key condition for the investors, although such an exemption also would require legislative approval next year.

It’s expected that the team owners, as the primary users, would cover the facility’s operating, maintenance and capital improvement costs.

Louis Jambois, president of the Port Authority, said they also may require the Met Council to ensure that the site is “clean,” or free of pollution, before the city leases it.

The agreement was passed unanimously by each body Wednesday after some overnight tinkering that deleted language that would have kept much of the information nonpublic. Adam Duininck, chair of the Met Council, said it was unnecessary and defeated their intention to open up the process rather than shield it.

“Sometimes the lawyers just get in the way,” he said.

Mayor Chris Coleman said he was seeking participants for a citizen advisory committee to provide input on design and development of a stadium and the broader site. It will begin meeting in December.

Although the momentum for a soccer stadium has shifted to St. Paul, a group of top Minneapolis officials met Wednesday to discuss the prospects for a stadium near downtown. The group was supposed to have presented its findings and recommendations to the City Council last month but missed its deadline.

“We are aware that St. Paul is moving ahead,” Mayor Betsy Hodges said. “But we are also moving ahead putting our plans together.”

Staff writer Eric Roper contributed to this report.