NEW YORK — Northeastern states struggling to rebuild hundreds of roads and dozens of bridges in the wake of Hurricane Irene are facing another natural threat: winter.

The end of construction season is fast approaching in New England and upstate New York. By November it will be too cold to lay asphalt, and by December snow and ice will cover the mountains, leaving towns dangerously isolated and possibly dissuading tourists during the region’s ski season. Vermont officials said Monday they are renting quickly built, military-style temporary bridges as a stopgap measure.

“We’re going to be into winter before we know it,” Vermont Gov. Peter Shumlin told reporters last week. “We’ve got a lot of highways to rebuild, bridges to rebuild, before snow starts to fly in Vermont.”

Raging floods gouged and closed more than 300 local roads and state routes in Vermont and damaged at least 22 bridges in the state, marooning people for days in at least 13 towns. Irene ripped another 150 roads in neighboring New York state. Some of the washed-out roads have gaping gullies 30 feet deep.

Road building experts say that if the work isn’t done by mid-November, winter’s cold, ice and snows will prevent any substantial progress until after the spring thaws.

The consequences could be serious: residents forced to make 30-mile detours — on mountain roads, some of them unpaved— to the nearest grocery store or doctor, businesses struggling for customers and a possible hit to the state’s all-important winter tourism.

“The window is short,” said Cathy Voyer, president of the Vermont chapter of the Associated General Contractors of America. “You can’t pour concrete, you can’t pour asphalt. Stabilizing cranes in the winter would be very difficult.”

Other states wrestling with post-Irene road repairs include New Hampshire, New Jersey, North Carolina and Virginia.

Brad Sant, vice president of safety for the American Road and Transportation Builders Association, predicted the affected Northern states will have to settle for “Band-Aid” repairs until the spring. Though the level of Irene’s road destruction is not unprecedented for a hurricane, “What makes this more challenging is the location of the destruction, being in the Northeast with those early, cold-weather conditions that are likely to come,” Sant said.

To help Vermont get an early start, U.S. Transportation Secretary Ray LaHood says he will authorize $5 million in “quick-release” rebuilding funds. Damage to the state’s federally funded highways alone is expected to top $125 million, LaHood said.

The state owns 360 feet of temporary bridge sections and plans to install them on key spans before winter, Michael Hedges, structures program manager at the Vermont Agency of Transportation, told the Associated Press.

It is also negotiating leases and rent-to-own contracts with three companies to bring in military-style “Bailey bridges,” Hedges said. The bridges, made up of 10-foot sections of metal decking, may have to serve for 4 or 5 years until the state can finish permanent repairs, he said.

In New York’s Adirondack Mountains, quiet summer brooks turned into torrents that ripped massive holes in the two primary routes around the winter destinations of Lake Placid, Whiteface Mountain and Saranac Lake — economic lifelines as the winter sports season approaches.

Both lanes of Route 73, the easiest way for people from the south to get to the mountains, were sliced clean through in some places, leaving jagged splinters of asphalt dangling over gravel, dirt and rushing water.

Gov. Andrew Cuomo estimated total damage to New York State at about $1 billion, but has not said how much of that is road damage.

In Vermont, some residents were forced to climb up and down ladders set in riverbeds where bridges were swept away. All-terrain vehicles ferried residents, food, water and medicines along muddy trails to get around gaping road washouts.

Deputy Transportation Secretary Sue Minter said officials still were unsure of the full extent — or cost — of the damage.

“We know that we have hidden hazards out there, things we may not even know about yet,” Minter said. “In some cases it could take years to get our roads to a standard that people are used to.”

In New Hampshire, officials have decided to wait until spring to build a permanent replacement for a washed-out bridge on U.S. Route 302 near the landmark Mount Washington Hotel. Crews were building a temporary bridge to serve until then, said Bill Boynton, a spokesman for the New Hampshire Department of Transportation.

“We just have to sort of button something up for the winter,” Boynton said.

Irene hit a region that already suffers from some of the worst roads in the region, according to a new study.

About 35 percent of Vermont’s rural roads were rated in poor condition before the storm, the highest percentage in the nation, according to a study released Thursday by the Washington-based TRIP think tank. In New Hampshire it’s 21 percent.

The region also has a high concentration of weak bridges, with about 15 percent of the spans in New York, New Hampshire and Maine rated as structurally deficient, according to the TRIP report. The study is based on data from the Federal Highway Administration.

New Jersey said it had finished almost all of its highway repairs by Friday. The worst damage was on Interstate 287, where the Rockaway River tore a hole the size of a tractor-trailer.

“The noise was atrocious,” said resident Theresa Kayhart, 51, as she peered down from a bluff overlooking the river on Friday. “You could hear the rumbling of the rocks moving away. I’ve never seen this river like that.”

Within days crews had filled in the hole with boulders and covered it with new asphalt.

Southern states were dealing with their own road troubles. In North Carolina, officials said they would lay a temporary, prefabricated bridge across the biggest hole in the Hatteras Island highway while the state Transportation Department plans long-term repairs.

Environmental groups say it makes no sense to rebuild a road on a moving barrier island. They have called for the state to build a 17-mile bridge that would bypass the area’s shifting beaches.

In Virginia, the state department of forestry said Friday it had removed about 2,800 trees that had blocked some 800 miles of roads.

On the upside, the storm has created a rush of new construction jobs as state and city officials go into “combat engineering” mode, said Boynton, the New Hampshire official.

And that rebuilding is likely to go on for a while, said John Horsley, executive director of the American Association of State Highway and Transportation Officials.

“This devastating attack by Mother Nature, with incredible flooding that took place, that’s going to set them back for years,” Horsley said.

Martha Waggoner in Raleigh, N.C.; Rik Stevens in Albany, N.Y.; and Lisa Rathke, John Curran and David Gram in Montpelier, Vt. contributed to this report.