Brian Fletcher's property backs up to a forest, which in these parts means his yard serves as an unofficial entryway for illegal immigrants sneaking into the United States from Canada.

From his porch, Fletcher sees shadowy figures carrying backpacks and "you-don't-know-what-else" emerge from the thicket of trees behind his house, and he rushes to alert border police. It doesn't take long for authorities to nab suspicious intruders in this northern Vermont village of less than 900 people, where customs stations outnumber grocery stores and enforcing international security is a way of life.

"It's all part of living on the border," says Fletcher, with a mild-mannered shrug.

Derby Line, like few other small towns across the nation, is literally spliced in two in places where Vermont collides with Quebec through the center of buildings and down the middle of streets. A painted black stripe runs through a historic library and opera house, demarcating national boundaries established more than a century ago, and homeowners in one nation must report to customs before visiting their neighbors in the other. Signs posted along roads leading into foreign territory instruct travelers in English and French to report to the nearest manned inspection station, creating a maze-like terrain where wrong turns can result in inadvertent border-jumping and possible arrest.

All this would be mere grist for the novelty mill if it were not for the events--or, as some here say, non-events--in late December. The Dec. 19 arrest of an Algerian man and Canadian woman at a border crossing east of here in Beecher Falls, Vt., coupled with the capture of an Algerian in Washington state on bomb-related charges, caused nationwide jitters and shifted attention from the hectic Mexican border to the 3,897-mile northern stretch known as the longest undefended frontier in the world.

Border stations have since been placed on heightened alert, and authorities are rethinking the "low risk" status of certain crossings in remote areas. In Vermont, agents who once worked solo have doubled up at the 14 official land checkpoints along the state's 100-mile northern perimeter. They also are manning continuously a rural port-of-entry in Pittsburg, N.H., formerly equipped after hours with only a video camera.

"It didn't feel so bad when it was out in Washington state, but when they pulled up at Beecher Falls, it got everyone extremely nervous," said Edward F. Cyr, who is based here as area port director for the U.S. Immigration and Naturalization Service. "I guess it's like the first time you get your car stolen or your pocket picked. You feel a lot more vulnerable."

Overall, New England represented a fraction--about 13 million--of the nearly 116 million inspections conducted at northern border checkpoints in the last budget year, according to INS. But that doesn't mean the hinterland of Vermont lacks its own brand of excitement.

Agents in this region detained a relatively high number of people over those 12 months, with about 2,300 apprehensions in New England and eastern New York, compared to 9,400 elsewhere along the border. Derby Line's low-slung facility on Interstate 91, about a 90-minute drive from Montreal, is one of the most frequented ports of entry in New England, INS figures show. Agents conducted more than 1 million inspections here last year, detaining up to 140 people and refusing entry to 1,000 others.

They found more than two dozen people, including 14 Chinese and 12 Pakistani nationals, hidden in a truck between rolls of newsprint during a spot check in September in what was the largest smuggling bust on the Vermont border. In February, a kidnapping and sexual assault suspect wanted in Connecticut was arrested here. And in July 1998, 27 Costa Ricans were found crammed into a van driving along a nearby dirt road.

Federal prosecutors in Burlington, Vt., alleged the Canadian woman arrested in December, Lucia Garofalo, had repeatedly tried to enter the United States with illegal immigrants, once attempting to cross the border in the middle of the night on an unguarded rural road west of here. Garofalo remains in custody without bail on charges of smuggling and passport violations.

Prosecutors, who have not charged Garofalo, 35, with any terrorist-related crimes, recently used telephone records to try to link her to Ahmed Ressam, the Algerian arrested with explosives in Washington state, and one of his accomplices. Garofalo has denied she is part of a terrorist conspiracy. Border agents, who noticed her route was unusual and itinerary vague, are not so sure. Said Cyr, "My boss told me the other day, 'We'll probably never know what we stopped, but I swear we were stopping something.' "

While Cyr and others want more resources to deter future gate-crashing, many Vermonters--including Gov. Howard Dean (D)--say they will fight to keep the border with their top economic partner as open as possible. Derby Line, in particular, shares some municipal services with its foreign neighbor and sees a steady flow of international tourists and commuters throughout the year. Given the weak Canadian dollar, it's not uncommon for villagers to take advantage of bargain groceries on the Quebec side while Canadians flock here to fill their vehicles with less expensive gas.

Nowhere are the advantages of cross-pollination and the desire to sustain amity more apparent than here at the Haskell Free Library and Opera House (motto: "Good Books/Good Neighbors"), an ornate turn-of-the-century Queen Anne revival building that physically straddles the border and has dual addresses and telephone numbers, and an international board of trustees. The front door leads to the Victorian homes and tree-lined streets of Derby Line, the back fire exit opens onto Rock Island, Quebec. The building has hosted three criminal trials involving smuggling of drugs, bombs and illegal immigrants with two judges--one sitting on each side of the border.

"We function here like one community," said Kim Prangley, a second-generation Haskell librarian with dual citizenship who lives in Canada. "So if they really tighten up on border crossings, it would make life tougher not only for the library, but people on both sides of the border."

Several residents said terrorism does not rank high on their list of daily concerns, which are more likely to include the lower drinking age in Canada and rowdy teenagers than the "so-called Algerian business." The fact that Garofalo and her companion were stopped at the border is a source of comfort to locals who have only to head down to the nearest flood-lit intersection for confirmation they are surrounded by law enforcement.

In nearby Beebe Plain, where the border cleaves a main avenue in half and makes neighborhood dinner parties tricky, an Alpine-style Canadian checkpoint building sits just a crosswalk away from its brick U.S. counterpart. Another inspection station stands here across from the Border Mini-Mart and next door to Village Hall. Border Patrol and state police officers, immigration agents and the sheriff live in town, too, and are active in organizations from the school board to the International Boundary Rotary Club.

As Fletcher, the village road supervisor, put it, "Can't get away with nothing in Derby Line."

CAPTION: INS agents at Derby Line, Vt., checkpoint on Interstate 91 conducted more than 1 million inspections last year, detaining about 140 people.

CAPTION: INS agent Burton McNeal questions Philip Lawandi of Montreal, who is crossing the border at Beebe Plain, Vt., on his way to his weekend home on one of the state's lakes.