PORTLAND — The public campaign to lure a Major League Soccer franchise to Portland was launched Wednesday, with plans that call for a new baseball stadium and renovations to the downtown’s PGE Park.

Merritt Paulson, who owns the Portland Timbers soccer team and the Portland Beavers minor league baseball team, is leading the effort to attract an MLS franchise. He was joined by Portland City Commissioner Randy Leonard and other community leaders in announcing the campaign.

Under the plans, a new stadium would be built in southeast Portland for the Beavers, the Triple-A affiliate of the San Diego Padres, who currently play at PGE Park.

PGE Park would in turn be renovated to fit the needs of an MLS team. The combined cost of the projects would be about $75 million.

Major League Soccer intends to expand to 18 teams for the 2011 season. Initial bids are due in mid-October, and MLS officials are expected to name the new franchise in early 2009.

MLS has 14 teams playing this season. Seattle will join in 2009 and a Philadelphia expansion team will debut in 2010. Among the areas expected to bid on a team are Atlanta, Las Vegas, Montreal, New York for a second team, Ottawa and Vancouver, British Columbia.

While full details of financing are not necessary in the initial bid, the city must show its commitment to back a team, Paulson said.

“It’s going to be tough. It’s going to be a tight timeline,” Paulson acknowledged. “But I’m confident we can get it done.”

Paulson would own the team, at a cost of $40 million, he said. The new stadium and the renovations to PGE Park would be funded through bonds to be paid for by ticket taxes.

The proposed site of the new 8,000-9,000 seat ballpark, called Lents Park, is already owned by the city.

“It does require the full faith and credit of the city to back those bonds,” said Leonard.

He said the economic benefit to the city would outweigh the risks.

“I am very comfortable that it will pay for itself,” he said.

Supporters point to the popularity of the Portland Timbers, who play a step below the MLS in the United Soccer League First Division, and the University of Portland’s women, who have won two national soccer championships.

“There’s no doubt in my mind that soccer is a phenomena in Portland, maybe more so than anywhere else in the United States,” Leonard said.

Supporters also launched a pair of Web sites to inform the public about the bids: www.mlstoportland.com and www.betterbeaversballpark.com.

MLS, now in its 13th season, has teams in Chicago, Colorado, Columbus, Dallas, Houston, Kansas City, two in Los Angeles, New York, New England, Salt Lake City, San Jose, Toronto and Washington, D.C.

Paulson said the existing Portland Timbers team would be moved if Portland wins an MLS team. The Portland State Vikings football team would still play home games at PGE Park.