IN 1997, in an essay on the facing page, Daniel Patrick Moynihan recounted the history, beginning in 1901, of efforts to rejuvenate Pennsylvania Avenue -- an effort that had finally succeeded, though he did not say so, mostly thanks to then-Sen. Moynihan himself. "There is work to be done. Where is there not? In particular we need more people living along the avenue and the nearby streets," Mr. Moynihan wrote. "But, all in all, not a bad century's work."

Which, adapted to the three-quarters of a century that he lived, might make a fitting epitaph for Mr. Moynihan, who died yesterday at 76. He pursued with distinction enough careers for half a dozen men of lesser talents and imagination: politician, presidential adviser, diplomat, author, professor, public intellectual. Daniel Patrick Moynihan was a man of large ideas in a city of tacticians, a visionary who nonetheless accomplished things, a partisan Democrat who worked productively for Republican presidents, a man of principle who got himself elected four times as U.S. senator from New York. He was a great internationalist who stoutly defended American interests while working to promote relations with the rest of the world, particularly India, where he served as ambassador and in which he maintained a great interest.

He was also a joker, a fighter, a wit and a provocateur. He could take a complex subject -- the slow rise of productivity in the service sector, say, and its implications for health care costs -- and explain it in ways that readers would not soon forget: "In 1793 to 'produce' a Mozart quartet required four persons, four stringed instruments, and, say, 35 minutes. To produce a Mozart quartet today requires -- four persons, four stringed instruments, 35 minutes. Productivity -- output per person per hour -- has hardly changed. You can play the 'Minute Waltz' in 50 seconds, but it isn't the same."

His thinking in the 1960s on welfare, family and race played a major role in the long-running debate about the country's programs of assistance to the poor. He was credited by many (and reviled by some) as a primary creator of the movement to reform the welfare system. He was accused of blaming the poor, when in fact he merely understood early on what is now widely acknowledged: the importance of coherent families. In any event, by the time major changes in welfare were approaching, he was against them: He thought the legislation would harm poor people. That was a characteristic Moynihan moment -- an example of his refusal to try to shape reality as he saw it into the mold of some abstract theory or doctrine.

This same quality served him well as ambassador to the United Nations, where he spoke bluntly and with vigor of the shortcomings of an institution very much in need of such talk. He saw that the 1975 resolution declaring Zionism to be a form of racism had its origins not in the Arab world but as "a calculated lie of the Communist Party of the Soviet Union." When the resolution was approved, Mr. Moynihan later wrote, "The place that had been the embodiment of liberal expectation after World War II had moved toward totalitarianism: the inversion of truth, the Big, Big Lie -- this was now the language of the General Assembly." But if Mr. Moynihan was unwilling to sugarcoat his words as a diplomat, he was also unwilling to give up on diplomacy or on international law.

Similarly, as a famous anti-communist, Mr. Moynihan was nonetheless even more famously a skeptic of CIA assessments of Soviet power. He was the first public figure -- way back in 1979 -- to predict that the Soviet Union might not hold together. He based his assessment on publicly available evidence -- demographics, the rotten condition of Moscow hotels -- and the total bewilderment of American intelligence agencies when communism did implode helped fuel Mr. Moynihan's lifelong antipathy toward government secrecy. He saw it as self-defeating as well as inimical to democracy. After 9/11 he warned against closing down what had to remain an open city. In his last essay for The Post, Mr. Moynihan decried the barriers and metal detectors proliferating in his beloved Ronald Reagan Building, at the central D.C. library and elsewhere downtown.

"Do we want to teach our children you must be checked by an armed guard in order to read a book?" he asked. "Or gaze in wonder at a giant Christmas tree? There are indeed buildings that need to be secured. And not a few. But there are places in the public square that do not need that. Might something go wrong? Yes. Nothing new. But the stability of the American National Government is not served by an intimidated citizenry."

The "public square" he loved best was the avenue he brought back to life. He lived right there on the avenue, in a place with a balcony, midway between the Capitol and the White House -- an institution in his own right, and one that cannot be replaced.