"EACH HONEST CALLING, each walk of life," James Bryant Conant once wrote, "has its own elite, its own aristocracy, based on excellence of performance." In the calling of diplomacy, David Bruce, who died Monday morning at the age of 79, was very nearly the embodiment of that aristocracy. He was, as Trollope said of Plantagenet Palliser, "a perfect gentleman." That is to say that he was, in the strict dictionary sense, "a man of good breeding, education and manners . . . civilized . . . sensitive . . . a man of independent income who does not work for a living." But that's only to begin with; it doesn't really describe the man, and still less his extraordinary career of public service. It is true that David Bruce did not need to work for a liging. And so, while he was from time to time a lawyer, a tobacco farmer, a banker and a business broker with eclectic interests (sugar plantations, race tracks, newspapers, parachute-manufacture, oil and a project for de-nicotinizing cigarettes), he worked almost all of his life for his country.

It began the day he left Princeton in 1917 as a sophomore at age 19 to enlist as a private in the U.S. Army in World War I, and it ended last year when he resigned from his post as American ambassador to the North Atlantic Treaty Organization - at the age of 78. And in between? There is no way to convey a sense of David Bruce's service in those intervening years without at least some brief resume: Chief of the Office of Strategic Services in Europe in World War II, Assistant Secretary of Commerce, administrator of the Marshall Plan for France, ambassador to France, Undersecretary of State, ambassador to West Germany, ambassador to Great Britain, and the head of the first U.S. liason office in Peking in 1973. And that's not complete: It doesn't, for example, take into account elective office: Mr. Bruce was a member at different times during his career of both the Maryland and Virginia Houses of Delegates.

The defeats and disappointments can be dealt with quickly - the triumphs take longer. There was the unrewarding 16-month tour as the U.S. representative to the Vietnam peace talks in Paris, beginning in 1970, when there was not much disposition on either side to compromise. And there was the shattering of a cherished dream when the French refused to ratify the European Defense Community for which he had labored hard as the American "observer" on an interim committee set up to advance this critical move toward European unity. For such unity as the Europeans have achieved, however, David Bruce deserves large credit. "It was Bruce who first singled out the Schuman Plan - the first realization of European unity - as a vital new idea, and mobilized American diplomacy to support it," wrote Theodore H. White in 1954.

As for the other triumphs, they were mostly quiet and difficult to measure, for they took the form of nothing more spectacular than the consistently effective, professional practice of diplomacy. David Bruce was not an ideologue. He was more often the engineer than the inventor of policy - he made things work. "Diplomacy is the management of international relations by negotiation," he once said. "It is not a system of moral philosophy." For him, the key to it was "the application of intelligence and tact," which he possessed in abundance. Most who knew him would add uncommon charm, intellectual curiosity, cultivation, consideration, patience - and toughness of mind.

In "A Thousand Days," Arther M. Schlesinger Jr. speaks of the "great confidence" that President Kennedy had in David Bruce's "steadiness of judgment." That's what it came down to, with six Presidents of both parties, over a span of more than 30 years. And that is why his country is so heavily in his debt.