Backers of bringing a Major League Baseball team to Portland say they have submitted formal proposals to purchase one of two potential ballpark sites close to downtown.

One is Portland Public Schools' headquarters, located in the Rose Quarter just north of the Moda Center complex and valued at more than $100 million, according to county assessor records.

Backers said only that the other location is an industrial site in Northwest Portland. Heavy manufacturing company Esco owns a large property like that -- on Northwest Vaughn Street between 24th Avenue and 26th Avenue -- and has said it wants to sell the portion that houses a large out-of-commission foundry. Its Vaughn Street property has an estimated value of $14 million, assessor records show.

The backers, operating as a company called Portland Diamond Project, declined to say how much they offered for each site. But their offers suggest they are serious about their ambitious plans to lure a pro baseball team to the Rose City, or claim a new team should the league expand.

The businessmen behind Portland Diamond Project hope to build a 32,000 seat stadium as part of a "vibrant, walkable" multi-use complex that could contain as many as 8,000 apartments, spokesman John McIssac said.

Portland Public Schools received the unsolicited offer to buy its headquarters from a real estate firm connected to Portland Diamond Project, district spokesman Dave Northfield said Tuesday. Northfield did not immediately respond to questions about how much real estate firm Trammell Crow offered for the district's property.

A $75,000 outside analysis conducted 13 years ago found that selling its headquarters and relocating its central functions would be a money-loser for the school district. But real estate conditions have changed in the years since.

Northfield said Superintendent Guadalupe Guerrero met twice recently with representatives of Portland Diamond Project, headed by retired Nike vice president Craig Cheek and former Trail Blazers announcer Mike Barrett.

"The superintendent listened and reiterated our core mission and priorities which focus on improving student outcomes," Northfield said of the meetings. He said the district is not "actively marketing" its headquarters property, but received and will consider an unsolicited offer from the group. The school board is scheduled to meet Thursday for its first discussion of the offer.

Until this week, Barrett, the former announcer, had been the public face of the resurrected MLB-to-Portland Portland effort. The Oregonian/OregonLive reported Monday that Cheek had formed Portland Diamond Project and filed paperwork with the Securities and Exchange Commission showing it sought to raise $6 million and had sold equity worth $500,000 to two unnamed buyers.

The company disclosed Wednesday that former state senator Jason Atkinson is also involved in the would-be management group, as a managing partner and strategic business director.

The company also said it has hired Kansas City-based Populous Architects, a firm that has designed many Major League ballparks, to design a stadium in partnership with Portland-based TVA Architects. The group also announced it has hired a New York-based attorney as its legal adviser.

Despite its organized approach, major hurdles remain for Portland Diamond Project. It will have to work out the details of land acquisition, public transit and parking, taxation, local politics, Major League Baseball regulations and more. None are small tasks. Together, they appear daunting.

And, there may be a conflicting plan for the Esco property. Backers envision it as a key piece of a separate project percolating inside City Hall to expand the Portland streetcar service in Northwest Portland.

The Transportation Bureau requested $370,000 in the upcoming budget to explore a streetcar expansion in Northwest Portland, and Portland Streetcar Inc. is working with Esco owners and other landowners on a concept to extend a streetcar line through the neighborhood.

Streetcar director Dan Bower said, thus far, he's had no discussion with any of the property owners about a baseball stadium, though the sport has been "tangential" to conversations because the Esco site was once home to a baseball stadium.

Bower said the streetcar extension would be roughly 2.4 miles and current cost estimates put the project at $80 million. A proposed loop route would go up Northwest 18th and 19th Avenue then head west on Northwest York and Wilson Streets, Bower said, with the loop connecting at Montgomery Park. That plan would call for extending York Street through the Esco site.

Others have sought to bring an MLB team to Portland, only to see their efforts flounder.

Then-Mayor Vera Katz convened a pro sports task force in 1996, which focused on site and design recommendations for a would-be MLB team in Portland. Len Bergstein, the task force's chairman, said Tuesday that the group found Portlanders have an appetite for pro baseball, but that finagling a stadium deal is tough.

"It's a complicated problem," said Bergstein, a political consultant. "You have to have an ownership team, a credible location, the financing."

In 2003, hoping to lure the Montreal Expos, the Oregon Legislature passed a bill approving $150 million in bonds for stadium construction in Portland. But the Montreal team moved to Washington, D.C.

A 2007 proposal to bring the Florida Marlins to Portland also faltered. Portland could not even permanently sustain its minor league team, the Beavers, which left town in 2010.

A major hiccup is public financing for stadium development. Many pro sports teams have construction of their facilities at least partially funded with taxpayer money. Bergstein said Portlanders have never held taxpayer financing of stadium deals in high esteem.

"I think there's a limited amount of public appetite towards publicly financing a baseball stadium," Berstein said. "I think the issues have become more complicated, not less complicated, since."

McIssac, the Portland Diamond Project spokesman, said the company does not intend to ask the Legislature or city to "create any new programs" to fund ballpark construction. Mayor Ted Wheeler told The Oregonian/OregonLive on Monday that he would not entertain a request for public funding of an MLB stadium.

-- Gordon R. Friedman

503-221-8209

Oregonian/OregonLive staffer Andrew Theen contributed reporting.