United Auto Workers negotiators at Ford Motor Co. have asked members to work the next 31 months without an increase in basic pay, hoping to stem the blood-letting that has laid off one-third of the UAW workforce at Ford amid huge financial losses.

Union negotiators preserved cost-of-living increases in the new tentative contract, reached Saturday night at Ford's Dearborn, Mich., headquarters, although there will be none for nine months and the deferred payments will not be fully paid until 1984.

But the concessions, if approved by the UAW's 170,000 Ford workers in the next few weeks, will still cost the typical union member several thousand dollars in gross pay this year, according to preliminary and unofficial estimates.

Neither Ford nor the UAW has indicated what they think the settlement is worth.

By giving up the traditional percentage increases in basic pay, and agreeing to settle only for the cost-of-living increases in the future, the UAW leadership has turned back the clock a long way.

Now the rank-and-file UAW members at Ford face the same tough issues that confronted UAW President Douglas A. Fraser and UAW Ford Vice President Donald Ephlin at the bargaining table.

How much to give back? What will it take to stop the erosion at Ford, which lost $2.5 billion in past two years? How to hold on to the remaining jobs at Ford when the company is looking harder than ever at cheaper foreign and non-union domestic suppliers for thousands of auto parts, from bolts to valves to complex transaxles for Ford's front-wheel-drive cars.

An initial inspection at the Ford-UAW agreement indicates a basic goal of saving the jobs of those still working.

In that, the UAW has followed the path of negotiators for the Teamsters Union and the United Food and Commercial Workers Union, who this year agreed to multiyear wage freezes to stop the loss of jobs to non-union competitors in the trucking and meat packing businesses.

There also are provisions aimed at helping laid-off workers. One is Ford's promise to resume payments of supplemental unemployment benefits to thousands of laid-off UAW members, many with less than 10 years' seniority. The payments were canceled when this benefit fund ran out of money.

Another is a stronger provision to restore seniority rights of jobless workers and protect their employment rights when business picks up.

The major features, however, seem directed at those still on the job.

* Ford is giving the UAW a guaranteed income program for high seniority workers. Those with 15 years' seniority who are laid off will receive 50 percent of their hourly wage rate until they reach age 62 or retire. This creates a powerful incentive for Ford to reduce its workforce through attrition rather than further layoffs.

* Ford approved early retirement provisions and strengthened the rights of senior workers who lose jobs to displace less-experienced workers at other plants.

* The other major "give-back" by the UAW negotiators was the elimination of nine paid personal holidays, a benefit that is in addition to customary vacation and holiday paid time off.

As Ephlin explained in a recent interview, the paid personal holidays were steps toward a primary UAW goal, the four-day week. By reducing the work week, the UAW was expanding job opportunities for a growing workforce, he said.

Those days are gone, probably for good. According to a Commerce Department analysis, a shrinking workforce lies ahead for the auto industry. Half or more of those now on indefinite layoff will never be recalled, the department predicts.

There will be few if any jobs for newcomers, Fraser has said with regret. The new agreement acknowledges that fact by providing lower pay and reduced benefits for new hires with no experience.

The proposed contract contains three features that are unusual, even remarkable by auto industry standards.

One is a profit-sharing plan that would be triggered if and when Ford's profits exceed 2.3 percent of sales revenue. The second is Ford's promise to establish pilot lifetime employment plans in two Ford plants to be chosen later. The third is Ford's promise not to close U.S. plants solely to shift business to other suppliers.

It is too early to say how much help Ford will get from the new contract. It offers less than the concessions granted by the UAW to Chrysler Corp. a year ago under great pressure from the government's loan guarantee board. Those concessions saved Chrysler $622 million and reduced the gross pay of the average Chrysler worker from $23,000 to $19,000.

But nearly 60 percent of Chrysler's surviving workforce voted for the cutbacks to save their jobs. And while the concessions did not guarantee Chrysler's future, it helped the company live another year.