ST. PAUL, Minn. — A report released Wednesday raised new questions about the cost and complications of building a Minnesota Vikings stadium on a heavily contaminated site in a Twin Cities suburb as the team said it saw nothing to derail the project and vowed to push harder than ever to get approval from reluctant state lawmakers.

The study, commissioned by Gov. Mark Dayton and prepared by the Metropolitan Council, called the goal of completing the Arden Hills stadium by 2015 "unrealistic" and said 2016 or 2017 was more likely. A longer construction timeframe would likely increase the current $1.1 billion price tag, the report said, threatening to tap out out a half-cent Ramsey County sales tax hike proposed to pay about a third of the total cost.

Despite the conclusions, Dayton administration officials said the report was meant to eliminate unknowns and get a deal moving. The lack of progress has raised fears about the Vikings' future in Minnesota, where the team is playing out the final year of its lease at the Metrodome.

"Our focus is to try to make the Ramsey County Arden Hills site work," said Ted Mondale, chairman of the Metropolitan Sports Facilities Commission and Dayton's point man on the stadium push.

Dayton, in a news release, refused to back either the Arden Hills site or any of three potential sites that would keep the team in downtown Minneapolis. He said if team officials want the suburban site they must indicate "whether they will accept the possibly longer timeline ... and whether they will pay for any resulting additional costs."

Vikings owner Zygi Wilf and his allies from the Ramsey County Board held a joint news conference and said they saw nothing in the report that would stop the project.

"The issues and concerns listed are solvable, and already being negotiated with state leaders," Wilf said. He didn't close the door on the team paying more than the $407 million they have pledged so far, with team vice president Lester Bagley saying the Vikings' ultimate contribution would be "somewhere north" of that amount.

That could be necessary to get the deal done. The report said that Ramsey County's current pledged contribution of $350 million could balloon as high as $408 million if site cleanup and construction goes slower than expected and drives up cost. And it doubted that the proposed half-cent sales tax would raise enough money to keep with a cost overrun of that size.

"The Ramsey County sales tax does not have the capacity to pick up cost overruns," Mondale said.

Commissioners Rafael Ortega and Tony Bennett, the board's two most vocal stadium backers, said the best way to eliminate overruns would be starting quickly on construction. Ortega said he believed the project is achievable "within the current parameters" but wouldn't say if he thought the county's tax base would be sufficient if costs go up.

"We are not there yet," Ortega said.

Late Tuesday, a county panel rejected a plan to put the sales tax increase to a countywide vote. The decision by the county Charter Commission does not preclude the possibility of a referendum, and key Republican legislative leaders have said they support such a vote.

The joint proposal by Ramsey County and the Vikings calls for transforming 430 acres of a polluted former Army ammunitions plant in Arden Hills into a stadium with ample parking for pregame tailgating plus future residential and commercial development.

The cost of the entire project is estimated at more than $1.1 billion. Besides the $350 million county share and the $407 million team contribution, the deal also calls for $300 million from the state and $15 million from the Sports Facilities Commission. The Met Council report noted that leaves $39 million in project costs unaccounted for.

The state's $300 million share would likely come from sales tax increases on game-related purchases like team merchandise or ticket surcharges. Backers say a gambling expansion with proceeds earmarked for stadium construction also remains a possibility.

Mondale said Dayton hoped by next week to convene a meeting with legislative backers of the project as well as party leaders in the House and Senate, as well as representatives of Ramsey County and the team. Dayton has not ruled out calling a special legislative session before the end of 2011 to vote on a stadium bill.

Rep. Morrie Lanning, the chief stadium bill sponsor in the House, said he hoped the Met Council report would build new momentum for a special session yet this year.

"We are working to line up the support," said Lanning, R-Moorhead. "But the governor is not going to call a special session unless he has assurances that the votes are there to pass this bill."