Rank-and-file United Auto Workers union members have overwhelmingly approved a historic concession contract that is expected to save Ford Motor Co. from $600 million to $1 billion in labor costs over the next 31 months.

The agreement, also designed to slow the march of Ford workers into unemployment lines, takes effect today, affecting about 171,000 of the company's U.S. employes, which includes about 60,000 on indefinite and temporary layoff.

Nearly 73 percent of the workers participating in the week-long ratification process that ended last night favored the new agreement. The vote was 46,683 to 15,933.

"We are very pleased that our employes have so convincingly approved our new labor contract," Philip Caldwell, Ford's chairman of the board, said after receiving formal notice of ratification in Dearborn, Mich., last night.

"There is, I am convinced, a clear understanding in our plants and at all levels throughout the company of what we all have to do to regain our national competitiveness. We are all in this battle," Caldwell said.

He said, "March 1 is a date we shall long remember as an important milestone" on the company's rocky road to recovery from $1.06 billion in losses in fiscal 1981, and a $1.7 billion setback in fiscal 1980.

UAW President Douglas Fraser, who failed to convince rank-and-file members to grant a concession contract to the General Motors Corp. in January, also was in an upbeat mood last night.

"We are extremely pleased at the margin of ratification" on the Ford agreement, Fraser said in a joint statement with Donald Ephlin, who heads the union's Ford division.

"It is clearly evident that our members at Ford understand and support the historic breakthroughs contained in the agreement, which will lead to greater security for themselves and their families," Fraser and Ephlin said.

What wasn't clear was whether, with the new Ford pact under their belts, UAW leaders would once again try their luck at GM. Both Fraser and GM Chairman Roger Smith have said they would like to restart the talks that stopped Jan. 28. But both are wary of a strong rank-and-file resistance at GM that was not evident in the Ford negotiations.

GM has announced plans to close eight plants since the collapse of negotiations with the UAW, adding 11,300 more workers to GM's already long layoff lists.

Smith over the weekend sent a "facts of life" letter to the company's estimated 600,000 hourly and salaried employes, asking them to help the company reduce its average $19.65 in hourly labor costs.

Any new negotiations with GM would have to begin soon to be meaningful. The company goes to regularly scheduled bargaining with the union in mid-July. Its current three-year contract with the union expires Sept. 14. Both Smith and Fraser agree that settling a few weeks before normal bargaining would serve little purpose.

The highlights of the ratified Ford-UAW agreement include:

* A 31-month basic wage freeze and the elimination of nine paid personal holidays per year, as well as the scrapping of bonuses for Sunday work.

* A two-year moratorium on additional plant closings. (This does not affect plant closings announced before the new agreement won tentative approval last month.)

* A profit-sharing plan, beginning in 1983 and contingent upon Ford's economic recovery.

* An "employment guarantee agreement" for workers with 15 years or more seniority. Under terms of the agreement, eligible laid off workers would receive 50 percent of their income, until they reach age 62 or retire.

* A provision entitling the union to reopen the concession contract if there is a major increase in Ford sales.