ST. PAUL — A wide gulf between how Republicans, Democrats and business groups want to tackle the state’s multibillion-dollar backlog of road and bridge repairs all but guarantees that what’s been billed as the biggest fight of the 2015 legislative session will live up to the hype. 

House Republicans unveiled a proposal Thursday that would tap a projected budget surplus and shave spending at the Department of Transportation to fund $750 million in repairs over the next four years. A package of tax hikes and fee increases favored by Gov. Mark Dayton and a coalition of Minnesota businesses would likely raise more than that every year for the next decade.

Dayton and top lawmakers in both chambers have set fixing the state’s ailing infrastructure network as their top priority.

At the heart of their differences is a disagreement between how large a bill the state may be facing. Conservative estimates put it around $2 billion, though it could be as much as $6 billion over the next decade. Move MN, a coalition of 200 businesses, cites other estimates that put the backlog at $20 billion over 20 years.

Move MN co-chair Margaret Donahoe called their package of proposed tax hikes released Thursday modest, but necessary to reliably fund transportation. It would generate an estimated $850 million annually.

“You can’t compete in a 21st-century economy with a 20th-century transportation system,” said coalition member Doug Peterson, president of the Minnesota’s farmer’s union.

The group wants to add a 6.5 percent sales tax to gasoline sales, in addition to the state’s current 28.5 cent per gallon tax. With prices at $2 per gallon, the change would add about $2 to a 14-gallon tank of gas. Move MN also wants legislators to increase sales taxes in the Twin Cities metro area by three-quarters of a cent, raise license tab fees and close a tax loophole for leased cars.

Dayton has pitched a similar plan to fix roads and bridges and make expansions. And though he told the Minnesota Chamber of Commerce Wednesday he’s open to alternatives, he’s stressed that any transportation package needs to generate reliable revenue — no short-term fixes.

Citing a desire to avoid another tax increase on Minnesota residents, Republicans who control the state House opted for a scaled-back plan that injects some money for transportation fixes.

It would transfer $200 million of the state’s projected $1 billion surplus for road repairs, require state transportation officials to spend nearly all of a special fund, and find budgetary savings that would be used for roads and highways.

Minority Leader Paul Thissen made clear House Democrats wouldn’t band with the GOP to support their plan, as Republicans did in 2008 to pass that transportation package.

“They’re already waving the white flag on a long-term transportation solution,” he said. “What they’re proposing isn’t even half a Band-Aid.”