DEARBORN, MICH., SEPT. 17 -- Ford Motor Co. and the United Auto Workers today agreed to a three-year contract that grants unprecedented job security to union workers and adopts a radically different approach to pay in the industry.

The tentative agreement, which must be ratified by the union membership, provides guaranteed employment during the life of the contract for most of the 104,000 workers at Ford's 85 plants around the nation. Ford has cut its work force by 44 percent since 1980.

In return, the UAW has agreed to work to reduce the number of job classifications and work rules on the factory floor, a move that would sharply increase productivity by allowing union members to do more than one job.

The contract also calls for an end to base pay increases in each year of the contract. Instead, the union agreed to a 3 percent increase in base pay the first year and a 3 percent bonus in each of the last two years. Unlike base pay increases, the bonus payments will not be used to determine fringe benefit payments such as pensions.

{In Toronto, Chrysler Corp. and the Canadian Auto Workers union reached a tentative agreement today that could end a costly strike and meet the union's key demand to tie pension increases to inflation. The agreement includes a six-year program based on a cost-of-living formula to calculate increases, subject to caps.

{Shortages of parts from the Canadian plants forced the layoff of about 2,000 U.S. Chrysler workers since the strike began Monday. The 10,000 workers at Chrysler Canada Ltd.'s four assembly and parts plants in Ontario will vote on the proposed three-year pact Saturday and Sunday.}

"What we have is a good agreement, one that truly breaks new ground on job security," UAW Vice President Stephen P. Yokich said of the Ford agreement. He predicted easy ratification.

Rank-and-file union leaders were equally optimistic. "We've got a heck of a good package here, one that we're proud and glad to recommend to our membership," said Orville Spencer, president of UAW Local 36, which represents 3,179 workers at Ford's single most profitable plant -- the Wixom, Mich., assembly facility, which builds luxury Lincolns.

"The union has achieved all of its objectives on job security," said former UAW president Douglas Fraser.

Company officials hailed the contract as historic.

Under the agreement, Ford will set up a "Guaranteed Employment Numbers" program that would guarantee the jobs of all current UAW-represented hourly workers at Ford's 85 facilities on a plant-by-plant basis; limit the loss of jobs through attrition by recalling one laid-off worker for every two jobs that become available through retirement, resignation or death; mandate the recall of workers who are laid off for economic reasons such as slow sales or an economic recession, and prohibit the scheduling of overtime at plants where workers are laid off.

The agreement also would raise the cost of overtime work by forcing the company to pay a penalty of $1.25 for each overtime hour worked. The money will be paid into a training fund. And to further discourage economic layoffs during the life of the agreement, the contract forbids the use of outside suppliers, foreign or domestic, to indefinitely extend the layoffs of production workers.

And finally, the new contract places a moratorium on plant closings.

Yokich said that working out the economics and mechanics of the job security proposal proved more difficult than both sides had expected. "This has been tough," he said.

"Ford employes all over this country should be proud of what has happened these past few days and of the people who have worked to put this historic document together. I just want to pay special tribute to all of them," Ford President Harold A. Poling said.

Poling and other Ford officials would not reveal the the cost of the settlement plan, which also folds into base wages 81 cents of the cost-of-living payments earned during the current contract. The other 5 cents in cost-of-living money earned during the current contract goes into a "float" to be applied to future COLA payments.

Retired UAW members will receive payment increases of up to $1,500 a year by the end of the contract.

The UAW chose Ford as a strike target two weeks ago. The strategy was to win a contract at Ford, then pressure General Motors Corp. into accepting a similar agreement. Contract talks at GM have been suspended pending the outcome of the Ford negotiations.

Several auto industry analysts said the contract announced today is tailor-made for Ford, which has sharply reduced its work force and substantially lowered its production costs. GM officials have said repeatedly that they will not accept any agreement that further undermines their competitive position.

Commenting on the Ford agreement, Alfred S. Warren Jr., GM's vice president for industrial relations, said, "Now that a tentative agreement has been reached at Ford, General Motors is prepared to resume intensive bargaining. Our goal is to reach a contract settlement which recognizes GM's specific needs and competitive challenges, and enhances job security of our employes."

Ford employes currently average about $24 in hourly pay. That figure actually worked out to $27.12 in 1986 because UAW-represented Ford workers received an average profit-sharing payment of $2,100.