Daniel Patrick Moynihan, 76, the scholar and senator, orator and author whose intellectual and political leadership did much to shape national policy on the major issues of his time, died yesterday at Washington Hospital Center, where he was recovering from an infection after an emergency appendectomy March 11.

A Democrat, he represented New York in the Senate for four terms before deciding not to seek reelection in 2000.Throughout his 24 years on Capitol Hill, Moynihan was one of the most trenchant and memorable voices in ongoing national debates on such issues as national security and Social Security, welfare reform and family matters.

He gained honor and recognition -- and often ignited controversy -- in many other roles as well: Harvard teacher and lecturer, ambassador to India and to the United Nations, adviser to presidents.

He was an advocate of renewing and preserving cities and their downtown buildings, and won renown in Washington as a champion of restoring Pennsylvania Avenue NW. His use of the phrase "benign neglect" to characterize an approach to racial policy that he was advocating set off a firestorm that smoldered for years. A 1965 report to President Lyndon B. Johnson created a major policy flap when Moynihan warned that the rising rate of out-of-wedlock births threatened the stability of black families.

A blend of the ivory tower and the big city streets, he combined gifts and qualities that were in many ways rare in American public life: a propensity to lecture fellow senators on sometimes abstruse topics, and a proven ability to win the votes of an often fractious and fragmented constituency.

An orator with an easy mastery of statistical fact and telling anecdote, he was a pungent phrasemaker, formidable in debate. In diagnosing the nation's social ills, he warned, in an oft-repeated phrase, that America was "defining deviancy down."

During Bill Clinton's presidency, debates over health care reform prompted Moynihan to say that threatening the nation's teaching hospitals was "a sin against the Holy Ghost."

Moynihan was a spokesman for the nation's mass transportation systems and for high culture, and demonstrated the ability to use the political system to obtain funds for both areas of interest.

In searching for parallels to his career -- with its combination of intellectual virtuosity and political leadership -- commentators cited the names of Woodrow Wilson and Thomas Jefferson.

Often seen as a politician ahead of his time, Moynihan was recognized as a liberal Democrat who was also a dedicated foe of communism, a combination that led to him being characterized as one of the first and most prominent of the so-called neoconservatives.

In 1980, he warned that the "Soviet empire" had begun to expand again, extending influence into Central America and bolstering its nuclear forces in a manner that was "mad and relentless." He was regarded as one of the first to foresee the decline of the Soviet "menace," and the eventual collapse of the communist empire.

Throughout his career, he maintained a vigorous interest in protecting the long-term vitality of American society by shoring up Social Security and reforming welfare. But he was also notable for his opposition to aspects of the welfare reform measures passed during the Clinton administration.

He expressed fear that some of these changes penalized helpless children, and when one measure was signed, he said: "Shame on the president."

Peering owlishly through horn-rimmed glasses, wearing a bow tie, a lock of hair tumbling across his forehead, he often displayed the slightly disheveled look that many considered to be distinctively professorial.

In his style of address, he was described at times as staccato, or stammering, or even spluttering. Sudden pauses were followed by rapid bursts of speech.

Those practices and mannerisms, which seemed suggestive of a scholar, led some to think he might not be well-suited to the gritty arts of legislative politics, the trading of favors and crafting of compromises.

Yet when he rose to become chairman of the Senate Finance Committee for a time in the Clinton administration, he was credited with signal service in guiding the administration's budget and tax measures to passage.

Moynihan was born in Tulsa to a father who worked in journalism and advertising. The father deserted the family while his son was still young, and his mother struggled to keep the family afloat financially as the family moved to Indiana and later New York.

After attending New York public and parochial schools, he enrolled at City College of New York in 1943, reportedly working for a time as a longshoreman and serving in the Navy during World War II. As part of officer training, the Navy sent him to Tufts University in Medford, Mass., where he received a bachelor's degree in 1948. He received a master's degree and a doctorate from the Fletcher School of Law and Diplomacy at Tufts.

He held a Fulbright fellowship at the London School of Economics and Political Science. In the 1950s, he became an aide to New York Gov. W. Averell Harriman.

His academic and vocational interests showed leanings toward politics, government and urban affairs. From 1959 to 1961, he was the director of Syracuse University's New York State Government Research Project. At one point, he ran in the Democratic primary for chairman of the New York City Council.

At the start of the Kennedy administration in 1961, he joined the Labor Department, starting as a special assistant to the secretary. He became assistant secretary for policy planning, serving through the early years of the Johnson administration.

After a sojourn in the academic world, he returned to Washington as an urban affairs adviser in the Nixon administration, and later served Presidents Richard M. Nixon and Gerald R. Ford as ambassador to India.

Ford later made him ambassador to the United Nations, where he served through 1976. While at the U.N., he denounced Soviet intransigence and expansionist policy, and challenged Third World policies that he viewed as motivated less by morality than by greed. He brushed aside criticisms of the United States, defying listeners to "find its equal."

He also impressed his future New York constituents with his vigorous defense of Israel.

An advertisement for his Senate race urged: "He spoke up for America. He'd speak up for New York." He was first elected to the Senate in 1976.

In office, he staked out the positions that came to be characterized as neoconservative: hostility to Soviet imperialism and compassion for the American poor.

Speaking in August 1980 at the Democratic National Convention that renominated Jimmy Carter, Moynihan warned of a re-expanding "Soviet empire."

In 1981, the first year of Ronald Reagan's administration, he opposed cuts passed by the Senate Budget Committee. "We have undone 30 years of social legislation in three days," he complained.

He wrote, co-wrote or contributed to many books, including "Beyond the Melting Pot: The Negroes, Puerto Ricans, Jews, Italians and Irish of New York City," on which he collaborated with Nathan Glazer.

He wrote on international law, on the role of ethnicity in international politics and on secrecy in government.

The Godkin lectures he gave at Harvard University in 1985 were published as "Family and a Nation."

A reviewer described the work as "a tale of the inability of politicians and social scientists to do something about the continuing destruction of the two-parent family," and the catastrophic consequences of this inability for the nation's social fabric.

That was an issue Moynihan had been identified with throughout his career in public life, and another review of the same book said that its true strength came not from the marshalling of statistics, but when the senator "talks to us from the heart."

A review of another of the senator's books said that it went far toward showing that "the story of modern American social policy and the story of Daniel Patrick Moynihan are one and the same."

In 2000, President Clinton awarded Moynihan the Medal of Freedom, the nation's highest civilian honor.

After leaving public office, Moynihan stayed active in politics, from campaigning on behalf of Hillary Rodham Clinton in her bid to succeed him in the Senate to his recent work as co-chairman of President Bush's Social Security commission. He also championed a plan to revitalize Manhattan's Pennsylvania Station.

While living in Washington, he and his wife, Elizabeth Brennan Moynihan, kept an apartment in one of the new buildings on Pennsylvania Avenue, which he found shockingly shabby when he arrived in the Kennedy years -- structures he had a major role in reviving.

Moynihan and his wife had three grown children, Timothy, Maura and John. They spent summers in an old, one-room schoolhouse in the upstate New York town of Pindars Corners, where he liked to write.

Daniel Patrick Moynihan mixed sharp intelligence and uncanny prescience. Daniel Patrick Moynihan greets his New York Senate successor, Hillary Rodham Clinton, in a New York City celebration in November 2000. Moynihan chose not to seek reelection after serving on Capitol Hill for nearly a quarter-century.