The 5,200 men and women who make the Ford Thunderbird, the Mercury Cougar and the hot-selling Econoline van put down their tools this week and began a strike that analysts say stems from pressures created by the auto industry's increasing drive to meet foreign competition.

The unusual strike, the first against Ford Motor Co. in eight years, was prompted by 23 union health and safety grievances revolving largely around charges that a Ford speed-up is forcing fewer people -- including many older workers -- to do more jobs under greater stress.

Industry experts say the strike reflects underlying tensions in the domestic automobile industry as it strives to cut labor costs to confront Japanese competition and imposes new demands on its work force to streamline production methods.

U.S. automakers see Japanese-style "flexible" job-combination -- having one worker take on multiple tasks rather than adhering to a rigid job definition -- as a key method for cutting as much as 15 percent of labor costs, said Lawrence Harbeck, a University of Michigan automotive research scientist.

"But it becomes very difficult to change established work patterns . . . . It's a lot easier to accomplish this in new plants," he said.

"Speed-up strikes" over production standards were common in the 1960s and 1970s, but the issue receded in light of the auto industry's decline and the rise of foreign competition," said Harley Shaiken, labor analyst at the Massachusetts Institute of Technology.

"It's long been a troublesome problem, a problem that never went away but got put on the back burner . . . . It's coming back, perhaps, in the ongoing push to cut costs," said Shaiken.

"For people who work on assembly lines, very small changes that look small to outsiders assume huge importance for workers, because every little change is repeated 60 to 70 times an hour, hour after hour."

The strike started Sunday and already has contributed to below-normal inventories of the three models at a time of resurgent auto sales. No talks are scheduled, and union sources say the walkout could last at least several weeks.

Ford spokesman Thomas Rhoades said the company is eager to resolve the strike, but he would not discuss the issues that led to it. "We do not negotiate these matters in the news media, but we hope for a quick resolution," he said.

Michael C. Pohorence, president of United Auto Workers Local 425, said Ford's program of "rebalancing" assembly-line jobs has added new tasks for most workers. As a result of that "job-combination" process and layoffs in recent years, 5,200 workers now are being asked to turn out up to 61 cars per hour compared to 7,200 who used to do essentially the same work five years ago, Pohorence said.

"People can't understand why we are striking when other auto workers are losing their jobs, but we see this as a question of human rights . . . that people's basic health and welfare are being threatened," said Pohorence, 45, a UAW officer since 1963.

Maintenance worker Coy Troutman, 35, agreed. "They're treating us like their robots is what it boils down to," he said. "They keep adding things on, so everybody here is doing a job-and-a-quarter or a job-and-a-half. They want the same quantity and quality with fewer people, and it's impossible."

Here, at the sprawling Lorain Assembly plant on Lake Erie, west of Cleveland, Ford has set a cost-cutting goal of 5.6 percent in labor costs this year, the UAW said.

That translates to a steady elimination of jobs and the addition of several new tasks for many of the remaining workers, such as John Triplett, 53, a hood-fitter who has worked for Ford for 25 years.

Triplett, who works mandatory overtime for a work week of up to 58 hours, installs 30 hoods an hour as he slowly walks backwards along the moving assembly line. Starting six months ago, his job was redesigned to include adjusting hood bumpers and removing fender-shields.

"I'll be honest," Triplett said. "I can still do this job. It's do-able, but it's just a lot harder now. I'd rather be on a 40-hour week, though. I'm lifting 30 hoods an hour, up and down, and those hoods get heavy before the day is over . . . . With a 40-hour week, your body gets a chance to recuperate. With 58 hours, it doesn't."

A major complaint that led to the strike is the lack of "emergency relief" for those on the assembly-line.

Employes contend that they are often forced to wait long periods before they can leave the line to use the bathroom or to see a doctor or nurse when they feel sick or suffer an injury. The union has received more than 500 written complaints this year about delays in getting relief, Pohorence said. Ford's contract provides for a regular morning and afternoon break, but employes can be disciplined for leaving the line at other times unless they are relieved by "utility floor men" whose job is to spell regulars.

Ford formerly had up to 150 utility workers to provide break time but now has 77, according to company data presented to the UAW. But the union claims the actual figure is 43 utility workers.

"As a result, we've got people who should be relieved in 10 to 30 minutes, but it's sometimes one, two or three hours, or not at all," said UAW negotiator Ace Adkins.

Because many workers are afraid of being disciplined, "we have people messing in their pants, and young ladies who actually hemorrhage," Adkins said, "but others who are bold enough to just walk off the job."

Such complaints, along with repeated protests about poor ventilation, heating, air conditioning and toxic fumes, have increased in recent months, Pohorence said. He said Ford appears unwilling to spend the money needed for physical improvements or staffing in the 25-year-old plant.

After four months of unsuccessful grievance meetings, the union called for a strike vote Aug. 1. More than 3,000 voted to strike by a margin of 92 percent, in the largest turnout in years, Pohorence said.

It is evident they are trying to automate our people, he said, " . . . People say autoworkers are a dying breed anyway. If we're dying, we at least want to die with dignity."