London — Fears that Britain may be heading for another ''winter of discontent'' have prompted Prime Minister Margaret Thatcher to opt for a secret weapon in her seven-month confrontation with the nation's striking miners.
She has arranged for a new face to present to the nation her government's case against the mine workers' Marxist president, Arthur Scargill.
This new person is Michael Eaton, the National Coal Board's area director in north Yorkshire. Himself a tough Yorkshireman like Mr. Scargill, Mr. Eaton is taking over from National Coal Board chairman Ian MacGregor the job of presenting the government's case for ending a strike that has so far cost the country hundreds of millions of pounds in lost revenue.
Mr. MacGregor will remain as board chairman, but Eaton's appointment reflects dismay within the coal industry and the Thatcher Cabinet over MacGregor's failure to best Scargill in the public-relations contest.
Some observers say Eaton's transfer will lead eventually to his assumption of the Coal Board chairman-ship. His current mandate is to improve the Coal Board's image and do all he can to avert a nationwide strike by mine supervisors that is due to begin Thursday.
The supervisors, who ensure that safety standards are maintained in coal fields where miners are still working, have not so far taken part in the strike. Following negotiations with MacGregor, whom they accused of taking an inflexible and abrasive line, the pit supervisors decided to strike.
Their move alarmed the Thatcher government and put heavy pressure on MacGregor who, after 13 months as Coal Board chairman, has displayed much impatience with Scargill and often seemed bitter in public pronouncements on the strike.
By alienating mine supervisors, government insiders say, MacGregor angered Mrs. Thatcher and gave Scargill an opportunity to gain public sympathy for his inflexible stand. Early in 1979 widespread industrial stoppages created a so-called ''winter of discontent'' that led to the downfall of Labour Prime Minister James Callaghan.
Thatcher wants to avert public disquiet over her handling of the coal strike. MacGregor's brusque and imperious ways convinced many observers he was not doing all he could to end the strike.
His defenders, however, note that he authorized a number of concessions offered to the National Union of Mine-workers, and that Scargill gave no ground at all. But Scargill was adept in presenting his case on television and radio, whereas Mac-Gregor appeared impatient and ill at ease.
The government made a shrewd move in giving Eaton his new job. He and Scargill, though adversaries, have operated together in Yorkshire for a dozen years and are said to respect each other.
Each speaks with the northern drawl of Yorkshire. Early in his career, Eaton, who trained as a coal mine engineer, went on strike in pursuit of a pay claim.
The government predicts that if the strike by pit supervisors goes ahead, the coal fields will probably shut down, creating a nationwide coal shortage by Christmas if not earlier. Thatcher's record of inflexibility could become a liability if it became apparent that the nation was facing a winter of privation.
In 1979 a wide range of public utilities shut down. Five years earlier, the Conservative prime minister, Edward Heath, lost a general election in which the key issue was the government's confrontation with striking coal miners.
Soon after Eaton took up his post, he said he wanted to find an honorable way out of the coal strike. He indicated that a lot of striking miners did not fully understand the Coal Board's policies, perhaps because of the way they had been articulated in the past.
''Everybody wanted an end to this strike,'' Eaton said, ''including Arthur Scargill. Mr. MacGregor will remain as chairman of the board, but it will be my job to communicate board policy to the public and within the industry.''
But it looks as though Eaton will be playing a much larger role than he, the government, or MacGregor will concede.
A government supporter said privately: ''Michael Eaton is our secret weapon. His task is to precipitate a fresh start in this long and damaging dispute before the political and economic consequences become too damaging for the government and the nation.''