When Bert du Mont and Ronald Caron close the door of their trailer parked off a remote logging road in the Maine woods these nights, they often listen to the sounds of the forest and feel pangs of fear.

DuMont and Caron are among several thousand Canadian loggers cutting timber in Maine this year for international pulp and paper companies. Their life at the far end of the nation's paper pipeline is hazardous and hard in the best of times, but lately it has been menaced by the eruption of labor strife in the wilderness.

The sleep of the two Canadians is troubled because Maine woodsmen - embittered by what they feel have been years of exploitation and unfair practices by the giant paper companies - have struck out at the presence of the foreigners.

They have begun to prowl the night, launching raids against the migrants to drive home their view that the companies are using the pool of foreign workers to depress pay and thwart organizing efforts of the traditionally poor Maine woodcutters.

On the night of Aug. 17, some 40 Americans arrived in pickup trucks at the logging camp of the St. Regis Paper Co. here and chased 19 Canadian loggers out of the gray shacks and trailers and into the woods. The Canadians were back the next day, unharmed but badly shaken.

St. Regis - whose Bucksport, Me., plant produces slick paper used by Time, Newsweek and other national magazines - promptly filed suit against eight woodsmen. It charged that intruders carrying axes, clubs and bats "terrorized" the occupants of the camp and threatened to burn down the buildings unless the Canadians fled.

The woodsmen named in the suit have denied that they participated in the incident, but the raid has heightened tension between the companies and the militant Maine Woodsmen Association, which began trying to organize the state's independent lumberjacks into a union in 1975.

The immediate cause of the friction is the use of foreign labor. But that issue is almost incidential to broader difficulties facing the woodsmen - in their challenge to the companies - most of them now huge multinationals. These companies have long dominated Maine's economy and politics through their ownership of sawmills, pulp and paper plants and vast timberlands.

Seven companies, together, own one-third of Maine's 19.7 million acres - half the state's forests. Land-management companies, which work closely with the paper companies, supervise another several million acres.

But the power of the companies in Maine is really rooted in an unusual labor system based on middlemen, private contractors and jobbers, and seen by its critics as almost feudal.

The companies issue permits for cutting wood on their land and usually stipulate that the cut wood must be sold to them. Since the companies control both the wood supply and the market for it, there is not much room for bargaining over the price, the woodsmen maintain.

A substantial amount of the woodcutting is performed by small, ostensibly independent contractors authorized by the companies to harvest timber on company plots.

In some cases the parent companies are further cushioned from direct involvement in the harvesting of the wood by brokers who serve as middlemen between the paper firms and the wood cutters.

In this contracting system, the contractors assume many of the financial risks. They pay workmen's compensation for their crews and amortize hundreds of thousands of dollars of investment in equipment, which typically includes trucks, loading machiens and rubber-tired "skidders" that drag trees from the forest.

The financial uncertainties are considerable. Woodcutting crews in Maine are paid on a piece-work basis, the same as fruit and vegetable pickers in Michigan or California. And, in turn, contractors are paid by the companies according to the amount of wood they deliver.

That can very depending on weather conditions and the quality of the timber made available by the company. Few of the private contractors are incorporated, and some have had their personal belongings seized to pay debts resulting from losses on their timber cutting operations.

In the view of Bill Butler, a man with red suspenders and muttonchop whiskers who is vice president of the Maine Woodsmen Association, the system is blatantly exploitive. "The companies don't practice forest management - they practice slavery," he snaps.

Calvin Thompson, a Lincoln, Maine, contractor who employs 40 American woodcutters, disagrees. He says, "The companies are good, if you work with them half-decent," although he adds that his operation lost money last winter when St. Regis assigned him to cut an area that was "too far back in the woods."

Woodsmen agree that the easy-going and independent life of woodcutters is changing rapidly, though. The nation's voracious demand for paper has increased the pressures on the paper companies to get more wood for their pulp mills, and these pressures have begun to be passed on to the woodcutters.

According to several woodsmen, the companies give their forest supervisors broad discretion over independent loggers - and this results in frictions. One logger complained that a company forester wouldn't assign him good trees until the logger called him "mister."

David Crane, a Vietnam combat veteran who has been working in the woods for seven years, complains, "They decide where to cut, how much to cut and what we get for it. We don't have anything to say about it. They treat us like we are the stupidest people on the earth. It's a great monopoly around here."

Officials of the Maine Woodsmen Association say it is a fiction that the private contractors are independent, and they are attempting to bring them into their organization.

The trouble at the St. Regis camp here came after an unexpected decision by the paper company to restrict wood purchases sharply from private contractors last month. St. Regis officials say the cuts were necessary because processes for making quality paper require wood that is no more than 30 days old and stocks had built up.

But many of the American woodcutters were angry because St. Regis continues to employ about 50 Canadian woodcutters in its crew of 100 loggers and skidder operators, while the private woodcutters were told to deliver no more than one day's load of wood a week.

Canadian lumberjacks have been working in the Maine woods for years, but they became the focus of the labor controversy only recently. At least 1,800 of the 4,000 woodcutters at work in Maine are Canadian. Of those, 1,200 are here on temporary visas and another 600 are bonded to work for specific logging contractors.

The U.S. Department of Labor certified the Canadians to work here after deciding that no Americans were available for the work and their presence would have no adverse effect.

Wayne Birmingham, the powerfully built president of the woodsmen organization, challenges the department's findings. He claims American woodsmen have sought the jobs and been turned down.

Norman Roderick of the Maine Employment Service Commission says the agency has received "numerous complaints" of the failure of unwillingness of employers - both companies and independent contractors - to hire American logers.

Some Canadians who have come here for years seem puzzled by the sudden hostility. Du Mont and Caron say they earn about $300 a week and spend some of that money returning home on weekends. They say they are not so sure they will be back in these forests again next year.

Birmingham maintains that the Canadians, many of whom speak only French, help perpetuate low piece rates, which in turn discourages Americans from becoming woodcutters. A new study by Jonathan Falk of New Haven on the Maine lumber industry claims that timber for sawmills in Maine sells for about a third the price of similar wood in the southern United States.

St. Regis insists there is a shortage of qualified American woodcutters. Public affairs manager John T. Gould Jr. says company loggers receive $12,000 to $15,000 a year plus allowances for providing their own chain saws and skidders. "As far as we're concerned, we pay an equitable rate for wood," he says.

Birmingham claims a more accurate figure for annual earnings of woodcutters would be $7,000.

Birmingham organized the woodsmen organization in 1975 after being fired from a lumber company in a dispute over weights. That same year the association threw up picket lines around five paper mills and briefly shut down one of the plants when union drivers hauling chemicals used in treating paper refused to cross the picket line.

A Maine judge subsequently issued an injunction against the picketing, but the woodsmen were surprised at their impact. "We never believed we could so something like that in Maine," said Butler.

Butler says the organization has 400 dues-paying members and 2,000 supporters.

Labor unions that had long neglected the woodsmen showed a sudden interest in organizing them after the association activities began in 1975. The United International Paperworkers Union, which already represents pulp and paper plant workers in Maine, suddenly sent organizers to the camps.

Birmingham claims that the paper companies quietly support the organizing efforts of the UIPU. So far the majority of the woodcutting members of that union are Canadian loggers who, Birmingham says, are vulnerable because of their status as foreigners.

That is an allegation that Eldon Hebert, a paperworkers union organizer, hotly denies, though he says that two-thirds of the 1,500 UIPU loggers are Canadians. "We're in the struggle of our life; it's the MFA that hasn't done a damn thing," says Hebert, who adds that dogs have been turned on union organizers at some camps.

The woodsmen also feel jeopardized by changes that are rapidly replacing men with machines in the Maine woods.

In the last few years companies have introduced mechanical harvesting machines that level airport-sized tracts to ankle height. These $150,000 tank-like machines carry blades that snip off tall trees like toothpicks and strip off their limbs in minutes.

"There's a tremendous revolution going on in the woods, and these renegades are worried about it," says St. Regis' Gould. "Every damn acre of the state is going to be working twice as hard as it ever did before."

Paper company officials are notably unsentimental about these changes. "Much of the independence woodsmen used to have is going to be lost as we go into more modern management techniques," says Gould.

The power of the paper companies is evident in the fact that many woodsmen are reluctant to criticize the companies publicly. Several woodsmen said they supported Birmingham's organization but asked not to be quoted to the effect.

It is this power that leads many woodsmen to feel they have their backs to the wall, and if explains why the nights have suddenly turned menacing in Maine's north woods.