Every Tuesday evening, a sleek black Cadillac limousine leaves the curb outside the downtown headquarters of the National Bank of Washington at 14th and G streets NW and weaves its way through Washington's dinnertime traffic to the offices and homes of the dozen men on the bank's executive loan committee.

There are no passengers on the plush seats of the chauffeured car, only a sheaf of papers comprising the minutes of the preceding week's committee meeting.

The minutes are delivered for each director's review before the next morning's meeting. The directors are instructed to return the documents to the bank lest a loose copy find its way elsewhere.

The executive life style comes with the appointment to the board. It means lunch at the exclusive University Club; dinner at the posh and stately Gaslight; soft, rich leather and deep-toned mahogany in the board room. It also means as much as $18,000 a year in extra income for attending the weekly two-hour meetings.

The board room of any bank is in the strictest sense an inner sanctum, where the decisions that shape a community are made in subdued light and rich furnishings. The National Bank of Washington's board room has undergone a radical reshuffling of characters in the last seven years, a virtual game of musical chairs orchestrated by leaders of the United Mine Workers of America, the bank's majority stockholder. UMW leaders have fired six top bank officers -- including two chairmen and two presidents -- in the past seven years.

The current chapter in the union's history began in December 1972, when Arnold Miller led a reform ticket called "Miners for Democracy" against the corrupt regime of W. A. (Tony) Boyle, the union boss who was convicted of ordering the murder of an earlier rival, Joseph A. Yablonski.

The bank, the union's largest single asset, became an issue in the heated 1972 campaign. True Davis, a former ambassador, aristocrat and socialite who ran the bank for Boyle, had been ridiculed by the reformers for his opulent life style and $142,000 bank salary. Within days of Boyle's defeat, the victorious Miller fired Davis by telegram from Charleston, W.Va.

The first wave of replacements came from the ranks of the Washington business establishment, bringing status and prestige to the bank, along with local business connections.

But with a second group of appointments, beginning in 1978 and 1979, the number of hand-picked union men and their friends placed on the board increased at a rate unprecedented in the bank's history:

First, Miller appointed himself to the board along with two other principal union officials, Vice President Sam Church Jr. and the new secretary-treasurer, Willard A. Esselstyn. For all practical purposes, the union men had virtually autocratic control of the bank, because in any test of power they voted 750,000 shares -- a full three-quarters of the bank's outstanding stock.

Ronald G. Nathan, a Miller-Church protege who had worked in the campaign as fund-raiser and strategist, also was appointed to the board and given the title of general counsel.

Nathan persuaded Miller to appoint to the board two of Nathan's friends, Irving B. Yoskowitz, who had practiced with Nathan briefly at Arnold & Porter, and Marvin L. Goldman, president of Washington's K-B Theatres chain, who had contributed $5,000 to Miller's reelection campaign.

At the same time, Church nominated his own close friend and campaign fund-raiser, Willie Runyon, a Baltimore ambulance company owner who came from a family of West Virginia coal miners. In 1979, Runyon nominated his close friend Wilson Lau, a Baltimore insurance executive, followed by Bethesda builder Nathan Landow, and Church added his union administrative assistant, Gary Callen. Corporate lawyer-lobbyist Thomas Hale Boggs Jr., a Democratic fund-raiser and a friend of Landow, also joined the board.

Arnold Miller resigned the union presidency in the fall of 1979 after a heart attack, and Church took over. Harry Huge, Church's personal attorney, negotiated Miller's resignation. Church subsequently appointed Reba Huge, the lawyer's wife, as an NBW director.

In recent months, Church has intensified the union's ironclad grip on the bank and, effectively, has been acting as chairman, running the bank through a small oversight committee he created, firing officers, appointing new board members and presiding over meetings of the full board of directors. Church has been unavailable for comment. He has denied in a public statement exerting any improper influence over the bank.