Peter Alexander Rupert Carrington will address Harvard's 336th Commencement exercises today, one day before his 67th birthday. The day's events will leave more of a mark on the graduating seniors than on one of the best and ablest diplomats in the Western Hemisphere.

Lord Carrington--the sixth baron to hold the 190-year-old British title--began his political career with his election to the Buckinghamshire County Council shortly after returning from World War II, during which he won a Military Cross for heroism. Since that time, the current Secretary General of the North Atlantic Treaty Organization (NATO) has served as high Commissioner of Australia, First Lord of the Admiralty, Secretary of Defense, Secretary of Energy, Chairman of the Conservative Party, and Foreign Secretary. He resigned the last position days after Argentina's 1982 invasion of the Falkland Islands as a matter of honor--because, he said, he had not foreseen the crisis, and because, others said, someone had to go.

Considered by fellow politicos and close observers to be one of England's most popular statesmen despite an affiliation with the increasingly unpopular Tory party, Lord Carrington was once considered a strong candidate for the job of Prime Minister. Although Carrington denied interest in the position, he enjoyed more widespread respect than the present P. M. Many also saw him as one of the two or three people that could tell Margaret Thatcher when it was time for her to step down.

Carrington's associates and followers all point to his successful conclusion of his negotiating effort to create a democratic Zimbabwe as his greatest accomplishment. The peer's effort came to fruition in late 1979, only after he convinced Thatcher to reverse her public position that the rebellion led by Robert Mugabe and Joshua Nkomo was mere terrorism. The settlement--which even Carrington and many members of his negotiating team had believed was impossible, they later said--perhaps could have been achieved only by someone with the unflagging pragmatism and clearheadedness of Carrington, who has demonstrated time and again the willingness to abandon political theory for realpolitik efficiency.

Ironically, it is this same cold-blooded rationality and distance from the political process that has been blamed for Carrington's gravest governmental missteps. The self-analytical Carrington once described himself as a product of privilege, and few would care to disagree with his assessment. Yet he once neglected the opportunity--available for half a year during the 1960s by virtue of an act of Parliament--to renounce his inherited peerage and run for the elected House of Commons. Nor, in all likelihood, would he seriously consider giving up his seat in the House of Lords for the sake of a constituency should the opportunity present itself once more, ventures Harvard Professor of Government Roderick MacFarquhar--who held a Labour seat in Commons--and other associates of Carrington. "He's an efficient, no-nonsense politician who never attempts to fool people by verbiage, but he's perhaps [indifferent] to the feelings of the public: he goes his own way."

Many inside and outside of the English government believe that a member of the House of Lords should not be a minister or member of the cabinet, let alone Prime Minister. Carrington often comes up as the prime counterexample to the demand of constituency for high-ranking ministers. In one famous episode, the Labour leader in the House of Lords (at a time when Carrington was Tory leader) was debating the abolishment of the House with a left-wing opponent at the Oxford Union, and one of the leftist's most effective arguments for the abolition of Lords was that it would allow Carrington to be Prime Minister.

But Carrington is content in the aristocrtic body, and some observers say his lack of ties to the voters is partially responsible for his lack of foresight regarding the Falklands crisis; he was away from London much of the time, and he was in Jerusalem just before the invasion. His greatest lapse, his friends and few detractors agree, came during his time as Conservative Party chairman. The coal miners were on strike, and Carrington played a key role in convincing Tory Prime Minister Edward Heath to call pivotal new elections. Heath called them a few weeks after Carrington wanted them, and lost. While people disagree as to the significance of the timing and while many believe the delay made Carrington blameless, it nevertheless cost him some of the deep and near-universal respect he has earned from fellow politicians and the general public at other times.

In general, his colleagues say, Carrington epitomizes the old school of patrician, moderate Toryism. His working relationship with Thatcher, a leader of a new Tory breed, as intent on fiscal austerity and hard-line anti-Soviet rhetoric as it is distrustful of the aristocracy, therefore came as a surprise to many. Carrington, in the words of Lowell House Government Tutor and Harkness Fellow Andrew Sullivan, "is the archetypal Tory `wet,'" the standard characterization for those in opposition to Thatcher's tight-fisted domestic policy.

"His main achievement during his tenure as Foreign Secretary was the suasion of Mrs. Thatcher that she had to deal with Mr. Mugabe in Zimbabwe. He should get enormous credit; they were absolutely against him," says MacFarquhar. "A minor but important human achievement was persuading Margaret Thatcher to accept the boat people" after visiting Hong Kong to guage their plight.

The prevailing interpretation of Carrington's peak years of power, when he was Foreign Secretary, has it that he had nearly full control of Britain's foriegn policy while avoiding confrontation with the Prime Minister on domestic issues. Some take issue with that analysis, however. "The simplistic image that he ran foreign policy for three years is not as true as it sounds," asserts Sullivan, a new-school Conservative who was president of the Oxford Union as an undergraduate.

Sullivan observes that neither Thatcher's anti-Soviet stance nor her "crucial" and positive relationship with President Reagan softened appreciably during Carrington's tenure. And while Carrington--a self-described European or Continentalist--was the official English delegate to the European Economic Community, Thatcher substantially reduced the country's contributions to the body. Sullivan also holds that Thatcher has moved decisively and permanently away from the sort of alliance that she had with Carrington: instead of reinstating him after the Falkands furor had cooled, she appointed Jeffrey Howe--a right-wing monetarist and close associate. Even among the wets, "Other people are calling the shots now," Sullivan says.

While Carrington's fall 1984 appointment as head of NATO hasn't been seen as a significant political comeback, policy analysts and U.S. officials have been impressed with his handling of the job. "What is very important is that he has challenged the nations of the alliance to look at the threat realistically. We are now examining the military position in a realistic fashion," comments Gen. Jack N. Merritt, the U.S. military representative to NATO. "He takes the long view; something NATO has never done."

Carrington's style of leadership differs markedly from his controversial and outspoken predecessor at NATO, Joseph Luns of the Netherlands. The alliance is "much less divisive now," according to Lecturer in Public Policy Richard N. Haass. "Many of the big, kind of doctrinal debates, about first use [of nuclear weapons] and pure defense [as opposed to 'forward' defense] have considerably toned down," agrees Stanley H. Hoffman, Dillon Professor of the Civilization of France.

Carrington arrived on the scene with the protestmarred deployment of Pershing II and Cruise missiles in several European countries. But all of the big decisions for the Year of the Missile had been made, and Carrington served chiefly as a steadying hand. Since then, NATO hasn't been in the media nearly as much. Some analysts see this lower profile as a tribute to Carrington: "The alliance doesn't make news when it works," says Haass. The minor crises--the dispute over action against Libya, the sporadic battling of Greece and Turkey, the near departure of Spain from NATO--haven't worsened, and internal discussions about tactical and strategic issues haven't deteriorated.

In contrast to Luns, who echoed Reagan's violently anti-Soviet rhetoric, Carrington has expressed "polite disagreement" with such a method. Nevertheless, he has toned down his own disapproval of the U.S. since his ascension to the leadership of the military resource-pooling of "15 sovereign nations, one of which is much more sovereign than the others," as Hoffman says. He adds that today's speech will be "one of the first times since he took the job that he'll have a chance to speak openly about Reagan's ideas and his own."