Editor’s Note – Guarding the U.S.-Canadian border in sparsely inhabited northern New England poses unique challenges. In a two-day series, Associated Press writers Clarke Canfield, Mike Recht and Wilson Ring document the history, the problems and what is being done to address them. Today: The scope of the problem and life in an unusual border town. Tuesday: Assessing the threat from Canada, and the payoff so far from heightened security.

LITTLETON – The only thing standing between Kai Libby and Canada is a steel barricade on a dirt road. But tire tracks around the barrier show just how easy it is to drive between the United States and Canada.

Since Sept. 11, Libby and other U.S. Border Patrol officers have dramatically stepped up their efforts to stop terrorists. But Libby concedes they can do only so much.

“For me to tell you it’s 100 percent secure would be foolish on my part,” he said.

The road here, at a place called Starkey Corners, is one of an estimated 140 unstaffed “back-road crossings” in Maine, six times the number of official ports of entry.

Maine’s 611-mile border with Canada includes rugged mountains, thick forests, lakes, rivers, fields and ocean. People cross illegally in cars and trucks, on foot and on snowshoes, in powerboats and canoes, on all-terrain vehicles and snowmobiles.

Drugs, cigarettes and liquor have been smuggled for as long as anyone can remember.

Nearly 9 million people and 4 million vehicles crossed last year from Canada into Maine.

After Sept. 11, the federal government vowed to assign more resources to the nation’s 3,987-mile northern border, the longest demilitarized boundary in the world.

In Maine, 20 more Border Patrol agents, 65 new Immigration and Naturalization Service employees and 45 new U.S. Customs Service inspectors will be arriving in the months ahead. Vermont and New Hampshire also will see staffing increases.

Customs now keeps two officers on duty 24 hours a day at all 22 official land entry points in Maine. Nine have limited hours, but remain staffed after hours to direct people to the nearest 24-hour station.

The agencies also have new tools. The Border Patrol has a new airplane and a new 25-foot powerboat with twin 220-horsepower engines.

Still, the border is vast and varied, and it’s easy to cross illegally on dirt logging roads in western Maine, across the St. John River in the north or through potato fields in the east. Border agents say people smuggling the painkiller OxyContin have taken to walking a railroad trestle across the St. Croix River into Calais.

In Hodgdon, David Landry lives on a dirt road that runs just a few feet from the border. He can throw a stone into Canada from his front door.

Landry said people used to cross the border on this road regularly. Occasionally, people would knock on his door to ask which country they were in.

Traffic on Landry’s road has slowed considerably since the early 1990s, when a barricade was erected between parallel dirt roads – one in Maine, the other in Canada. A camera on a utility pole monitors traffic and sends pictures to the Border Patrol’s sector headquarters.

Since Sept. 11, the Border Patrol is paying more attention to who uses the road, and so is Landry.

He now locks all his doors at night, and said he wouldn’t hesitate to report someone crossing illegally. Previously, he would let it go with a shrug.

“It makes you a little nervous about where you are if terrorists decided to come across,” he said.

Farther north, in Fort Fairfield, the Aroostook County Golf Club’s parking lot and pro shop are in Maine, but the course itself is in Canada. Canadians drive into Maine unchecked to get to the parking lot. When they leave, a sign warns them to turn right – “United States law prohibits turning left” – to Canada. But if they turn left, nobody’s there to stop them.

Here, too, there is a monitoring camera on a pole. But anyone making an illegal left could be on a well-traveled road within minutes.

Many of the back-road crossings now have barricades to deter inadvertent border crossings. Gone are “honor system” crossings at which people were allowed to enter with the understanding that they would drive to the nearest official entry point to check in.

In the woods, the border is marked by a 20-foot swath like a power line, but without the towers or lines.

Several crossings have cameras. The majority have sensors that detect motion, heat or metal to alert agents to illegal crossings, Libby said.

The Border Patrol now uses four-wheel-drive vehicles, ATVs, snowmobiles and boats to patrol. The immigration service and customs use sophisticated computers for background checks on people entering the state, and U.S. agencies have better communications with the Royal Canadian Mounted Police and other Canadian agencies.

But crossing the border easily is a way of life here, and more than $5 billion worth of goods – wood and wood products, industrial machinery, auto parts and fish – cross between Maine and Canada each year.

Chris Sands, director of the Canada Project at the Center for Strategic and International Studies in Washington, D.C., said the government should focus on identifying and nabbing terrorists before they reach the border.

“With so much wilderness, the odds of creating an enforceable border are pretty low. A really impenetrable border is something beyond something we can cook up,” Sands said.