A REPORTER once asked Gen. George C. Marshall to name the indispensable qualities of a public servant. Marshall answered thus: "Courage. Wisdom. Tolerance. An understanding of the democratic procedures."

The remark was in character for this austere public servant. One of his old army colleagues, Lt. Gen. Marshall Carter, recalled in 1980 that he had never once heard Marshall ask in regard to an official decision, "What's in it for me? How am I going to look?"

Marshall would have trouble recognizing Washington today. There are still a few relics of his era around town: Paul Nitze at the State Department and a handful of lawyers, generals and ex-officials. But the capital today is a far different place than it was in the 1940s, with a different cast of characters and a different set of values. The patrician liberalism of Marshall's day is long gone, replaced by a populist conservatism that is at once more democratic and more enthralled by money and power.

Sadly, the public-service ethic that Marshall embodied is also vanishing. This decline is highlighted by some of the extreme cases of the 1980s -- it is difficult to imagine Marshall having kind words for Michael Deaver or Edwin Meese, for example. But the changes are deeper and more fundamental than a simple list of scandals and indiscretions, which could be compiled as easily for the Truman administration as for the Reaganites. What has happened seems almost a change in culture, a change in the notion of what constitutes acceptable behavior.

This change is illustrated as much by David Stockman, who was one of the administration's more capable officials, as by Deaver. Both rushed with shameless haste to profit from their public service, and it is Stockman, with his multi-million-dollar book and banking ventures, who at this point seems most likely to cash in big.

Marshall's generation regarded government service as a virtuous endeavour, something that was worth the personal and financial sacrifices. These Establishment civil servants could afford to make the gesture, of course, since so many of them were already rich. There was something European about this class of patrician civil servants and their noblesse oblige ethic. That may be why the rest of the country grew to resent them.

In today's Washington, in contrast, government service is instrumental -- a way to make contacts, build a reputation, make a reasonable salary -- rather than an end in itself. The prevailing ideology these days is that virtuous and rewarding work takes place in the marketplace, in the "private sector." Public life is regarded as a regrettable intrusion into this private sphere, and the institutions of government are seen as a necessary evil, rather than a way to do good.

The decline of public service has coincided with other dramatic changes in Washington. It's hard to know what has caused what, but these changes are part of the story of how George Marshall's Washington became the city of Stockman and Deaver. Here is a sampling of statistical and anecdotal evidence about the great transformation:

*Rising Salaries. The decline of the public-service ethic has been accompanied by significant increases in pay. The salary rate for a Cabinet officer last year was $86,200, for a subcabinet officer $75,100 -- not a fortune, but not a hardship wage, either.

The big change in pay scales for senior officials, interestingly enough, came in the late 1960s -- at about the same time that the Establishment began to crumble because of Vietnam. The salary of a cabinet officer in 1964 was $25,000, only $2,500 more than what he would have earned in 1949! Pay increased slightly in 1964, to $35,000 a year. But the big jump didn't come until 1969, when Cabinet pay rose to $60,000.

*Growing Affluence. Once upon a time, Washington really was the sleepy little town on the Potomac that old-timers remember. No more. According to the April issue of Washingtonian magazine, the D.C. area is now the richest and best-educated metropolitan area in the nation.

Charles Peters of The Washington Monthly notes that one index of the city's growing affluence is the increase in the number of French restaurants during the past two decades. Twenty years ago, Washingtonian magazine could find only seven worth mentioning in its May 1966 restaurant guide; this year, the Yellow Pages lists 47 French bistros in the Washington area.

*The Lobbying Boom. The most obvious change is the explosion of political action committees. According to the Federal Election Commission, the number of PACs increased more than sixfold in the last decade, from 608 in 1974 to 3,992 last year. The increase in PAC contributions to House and Senate races was even greater, jumping from $12.5 million in 1974 to $105.3 million in 1984.

With the flood of PAC money have come more lawyers and lobbyists. The D.C. Bar Association says its membership more than doubled over the last decade, from 21,429 members in early 1976 to 44,518 members last month. The number of registered lobbyists has also more than doubled since 1976, according to Time magazine, rising from 3,420 to 8,800. These figures are understated, Time stresses, noting that "most experts put the influence-peddling population at about 20,000, or more than 30 for every member of Congress."

*Playing by Congressional Rules. In Marshall's days, senior civil servants tended to be drawn from the great law firms and banking houses of Wall Street, which were the bullpen of the Establishment. The recruiting ground shifted during the 1960s and '70s to universities. Consider the roster of university-bred national security advisers: McGeorge Bundy, Walt Rostow, Henry Kissinger, Zbigniew Brzezinski.

The Reagan administration's national-security bullpen has been the Congress, or more precisely, staff aides to conservative members of Congress. The former staffers who made good include: assistant secretary of defense Richard Perle; deputy national security adviser Donald Fortier; NSC arms-control specialist Ron Lehman; NSC intelligence specialist Ken DeGraffenreid, and former national security adviser Robert McFarlane.

Perle's tactics -- ethically acceptable but somewhat bare-knuckled compared to Marshall's day -- exemplifys the congressional staff man's approach to policy: Go to the wall on every major issue; cultivate the news media to advance your personal agenda; maintain loyalty to your boss, rather than to larger institutions; treat every issue as a test of political strength; compromise only at the last minute. This approach, skillfully used by Perle and others, helped paralyze administration arms-control and foreign policy during much of the past six years.

*The Dearth of Resignations. There was a time when it was typical for officials who disagreed with administration policy, or who felt their useful service had come to an end, to do the proper thing and resign.

Paul Nitze, for example, decided to resign as SALT negotiator in 1974 because he felt the Nixon administration was too preoccupied with Watergate to do any serious bargaining.

"I sat down and wrote a letter to the president requesting permission to resign," Nitze recalls. When Nitze didn't receive a response, he decided to send a letter unilaterally terminating his employment. (He recalls that as he left for the office that day to write his letter of resignation, his wife Phyllis called out from the window and said: "Paul, keep it short.")

Contrast Nitze's willingness to resign with the approach of Stockman, who by his own account remained in the Reagan administration for more than four years after he concluded that its fiscal policies would have disastrous effects on the economy.

In a conversation last year, Nitze summed up the world of George Marshall -- the world of public service we have lost -- this way:

"There was never a more honest government in the world than in World War II and after. I have never seen such a panoply of first-class people who never thought of putting their interests before the nation's. We were all spoiled during that period. Dean Acheson, John McCloy, Robert Lovett. But it wasn't just the Establishment. People at every level of government. They wouldn't tolerate such things as we see today."