For the fourth time in the last five years, executives of beleaguered Wheeling-Pittsburgh Steel Corp. have turned to their workers for concessions and yesterday, they waited to see if the 11,000 workers would approve reductions in labor costs totaling about $35 million over the next 19 months.

The concessions on which steelworkers voted yesterday are designed to help the nation's eighth-largest steel company keep its head above water and meet to its repayment schedule on nearly $360 million it has borrowed for modernization of its aging plants.

Even if concessions are apoproved, however, Wheeling-Pittsburgh's future is far from secure unless there is a substantial pickup in demand for steel, according to one Wall Street analyst.

While all steel companies are hurting as a result of the severe recession, Wheeling-Pittsburgh has been hit harder than most.

It sells nearly all its steel to the three industries that have suffered the most and the longest in the economic slide: automobiles, construction and appliances. Wheeling-Pittsburgh is operating at not much more than 39 percent of its capacity, according to Joseph Scalise, vice president for industrial relations.

By contrast, the steel industry as a whole is operating at about 60 percent of capacity, according to Karlis M. Kirsis, director of world steel dynamics for the brokerage firm Paine Webber Mitchell Hutchins Inc.

"They can't continue to operate at 39 percent of capacity," according to Charles Bradford, steel analyst for Merrill Lynch Pierce Fenner & Smith.

U.S. companies are expected to ship about 75 million tons of steel this year, Kirsis said, compared with 100 million tons in 1979, the last reasonable year the steel industry had. In 1973 steel makers in the United States shipped 112 million tons.

Wheeling-Pittsburgh, despite its major modernization effort, faces long-run problems if the labor concessions give it enough breathing time to survive the current recession.

All of the company's plants are located in West Virginia, Pennsylvania and Ohio, far from the nation's major steel users. Furthermore, its plants are older and smaller than those of many of its competitors, which makes it more difficult for Wheeling-Pittsburgh to efficiently organize its plants.

Wheeling-Pittsburgh is building a new rail mill--helped by a controversial $150 million government loan--and is planning to add tubular products to its capability. But the demand for rails has dropped sharply and the declining price of oil has put a sudden vise on demand for tubular goods--which were the only bright spot in the steel industry last year.

The concessions sought by the company include giving back a week's vacation this year and next, 13 paid holidays over the next 21 months and increases scheduled for Aug. 1 in return for equal amounts of preferred stock in the company.

Scalise said the money saved by concessions will not be used to build new facilities.

"Building in West Virginia made sense 50 years ago, it doesn't today. The freight costs and the costs of bringing in raw materials like ore and coal is too high," according to David Healey, an analyst with the brokerage firm Drexel Burnham Lambert Inc.

One of the major problems for Wheeling-Pittsburgh will be General Motors Corp.'s buying policies. GM, which buys its steel at list price from 10 domestic suppliers, has announced that it wants to buy steel at the lowest price. Many analysts feel that GM also will cut out three of its suppliers to enable the remaining steel makers to have enough GM business to operate efficiently.

"Does Wheeling-Pittsburgh bid low enough to keep GM but continue to lose money on each ton of steel it makes? Or does it run the risk of losing all GM business?" a major steel analyst said.