The National Mediation Board yesterday rejected Eastern Airlines' request for mediation of the firm's demand that its pilots make wage concessions, suggesting instead that negotations between the sides be resumed on Thursday.

Eastern already is facing a threatened strike from flight attendants unless they are given raises that were promised earlier.

Meanwhile, leaders of Alaska Airlines' 2,500 union workers have rejected a call by the company for $20 million in voluntary wage cuts, and Ozark Air Lines has asked its employes to make more than $30 million worth of concessions next year.

Eastern's pilots are disputing the company's request for pay cuts and a multitiered pay schedule for new pilots.

On Friday, the mediation board released Eastern and its flight attendants from federally mediated contract negotiations. That set off a 30-day cooling-off period and paved the way for a possible strike Jan. 20.

An Eastern spokesman said the airline sought the release from mediation to speed up negotiations. "We were negotiating and getting nowhere," he said.

Robert Callahan, president of the flight attendants union, charged the company is trying to force a walkout.

But both sides said they are hopeful a wage pact will be reached before the cooling-off period expires.

After recording a $46.4 million profit in the first six months of 1985, Eastern lost $28.6 million in the third quarter, and analysts are predicting its fourth-quarter losses could reach $65 million.

Meanwhile, bleeding red ink from the ongoing West Coast fare war, Alaska Airlines earlier this month asked the unions representing its pilots, flight attendants, mechanics and other ground workers to consider wage cuts ranging from 20 to 26 percent. "My impression is that basically they didn't care for it at all," said Lou Cancelmi, a spokesman for Alaska Airlines.

The unions did accept a company suggestion that they submit proposals of their own for reducing costs. The initial rejection of the wage cut idea, however, means the airline won't meet its goal of instituting a cost-cutting plan by Jan. 1.

Alaska Airlines reported on Dec. 12 that it lost $4.1 million on its operations in October and November. The losses represent a sharp downturn for a company that had a $25.6 million profit during the first nine months of the year.

As for St. Louis-based Ozark, executives told their unions at a recent meeting that the airline needs the concessions to become competitive.

Ozark has above-average labor costs, airline industry analysts say, and lost $2.42 million in the last quarter partly because of pressure from lower-cost competitors.