TORONTO, AUG. 24 -- In Canada's first national rail strike in 14 years, passenger and cargo services were paralyzed today when the 48,000 workers for the two main railways walked off their jobs, posing serious economic risks.

Expectations that the walkout may be a long one raised strong fears here because of the dependence of grain farmers, coal producers and foresters on trains to move their goods. About 30 percent of all exports to the United States, Canada's major trading partner, move by railroad. Some commodities producers said they will curb production and begin laying off workers if the strike lasts more than 10 days.

"This is another nail in the coffin of the people who work the land," said Anne Briscoe, a coordinator of the National Farmers' Union.

The strike disrupted the plans of summer tourists and left stranded thousands of commuters in suburban Montreal and Toronto, who normally travel to work each day by train.

The formal walkout just after midnight had been preceded by several days of scattered wildcat strikes across the country. A federal mediator brought into the talks in Montreal had tried unsuccessfully for a week to head off the job action.

"We've been jerked around," chief union negotiator Armand Passaretti told reporters in Montreal, explaining why he was taking workers out.

"The unions are unwilling or unable to come to grips with the realities of our changing environment," said Robert Colosimo, chief negotiator for privately owned CP Rail, which along with rival government-owned Canadian National Rail, moves virtually all freight in Canada.

At issue are a host of longstanding work rules that require, among other things, that an engineer, conductor and brakeman be on all trains. The wage system is based on the number of miles traveled, not hours worked. In addition, the railroads are attempting to alter past agreements so that they can contract with outside firms for some maintenance tasks.

The unions are seeking protection against layoffs for all workers with at least four years' service, regardless of whether their jobs become obsolete -- and even if rail traffic declines. At present, the unions have a guarantee that workers with eight years on the job cannot be laid off because of technological changes.

"To suggest that we can give employment security to our employes when traffic is not available for whatever reason . . . would be economic suicide," Canadian National President Ron Lawless told The Associated Press in an interview hours before the strike began.

Canadian unions, which have grown over the past decade as American unions have lost their former share of the labor force, have tended to be far more militant and less willing to roll back gains won in previous contracts than their U.S. counterparts.

Dire predictions of economic troubles tend not to be taken as seriously in Canada as they sometimes are in the United States because of the feeling among workers that companies in trouble can, and often do, receive financial aid from the government. Canadian railroads have received generous subsidies over the years.

The 48,000 railroad workers are represented by nine unions that make up the Associated Railway Unions. They have been without a contract since December. The last time that railworkers walked off the job was in 1973. Parliament ended that dispute, a series of rotating strikes, with legislation ordering them back to work. A contract was hammered out through arbitration.

Federal Transportation Minister John Crosbie suggested that the current government might take similar measures. In a carefully worded statement today, he said the rail strike would be reviewed "to protect the public interest."

"The strike is very costly, not only for the parties immediately involved, but in this case for all of Canada," Crosbie said.

There was a run on trucking firms in Canada as producers and manufacturers attempted to find alternatives. But users have found that trucks are uneconomical for Canada's bulk cargo, such as coal and grain, and cannot easily travel on highways through the Canadian Rockies, for example.