NEW YORK - Economist Paul A. Samuelson, who wrote a textbook read by millions of college students, helped shape tax policy in the Kennedy administration, and won a Nobel Prize for his effort to bring mathematical analysis into economics, died yesterday.

Mr. Samuelson, 94, who taught for decades at Massachusetts Institute of Technology, died at home in Belmont, Mass., the school said in a statement announcing his death.

President Obama's chief economic adviser, Lawrence Summers, is his nephew.

In 1970, Mr. Samuelson became just the second person, and first American, to win the Nobel Memorial Prize in Economic Sciences, created in 1968 by the Central Bank of Sweden. The other Nobels have been awarded since 1901.

The award citation said he "has done more than any other contemporary economist to raise the level of scientific analysis in economic theory."

A 1970 New York Times profile said his mind "possesses the agility of a Nijinsky and the endurance of a cross-country runner."

Mr. Samuelson was a liberal, and, like many of his generation, a follower of British economist John Maynard Keynes, who proposed that a nation needed an activist government that could foster low unemployment by steering tax and monetary policies, even if it meant deficit spending at times.

"In the old-fashioned laissez-faire economy, prosperity was indeed a fragile blossom," he wrote in a 1970 article for the New York Times.

He was among a circle of JFK advisers, which also included John Kenneth Galbraith and Walter Heller, who led Kennedy to recommend a historic income tax cut that Congress passed in early 1964, three months after the president was assassinated.

"A temporary reduction in tax rates on individual incomes can be a powerful weapon against recession," Mr. Samuelson wrote in a report to Kennedy in early 1961.

The cut was widely credited with helping foster the 1960s economic boom.

It was Mr. Samuelson's work as an educator, both in the classroom and as a textbook author, that may have been his most influential role.

College students have been reading Economics since the late 1940s. It had its roots in a short text he put together to use in his MIT classes. It is now in its 19th edition; the more recent editions were cowritten by William D. Nordhaus of Yale.

The book has sold more than four million copies in more than 40 languages.

In a 1998 AP interview, Mr. Samuelson said his aim had been to make economics "understandable and enjoyable."

Publisher McGraw-Hill paid an unusual tribute in 1997 by reissuing the original 1948 edition, reproducing not just the original text but the illustrations and layout.

That same year, in a column by Mark Skousen titled "Welcome back, Professor," Forbes magazine praised Mr. Samuelson for gradually turning away in his textbook from pure Keynesianism toward more traditional economic theory.

For the more casual reader, he wrote a column for Newsweek magazine from 1966 to 1981.

Born in Gary, Ind., in 1915, Mr. Samuelson graduated from the University of Chicago in 1935 and earned master's and doctoral degrees from Harvard. He joined the MIT faculty in 1940.

He married Marion Crawford, a fellow economist, in 1938, and he credited her with helping in his early research. They had six children: Jane, Margaret, William, John, Paul, and Robert. (The Robert Samuelson who writes a business column for Newsweek is no relation to the Nobel winner.)

Marion Crawford Samuelson died of cancer in 1978 at age 62. In 1981, Mr. Samuelson married Risha Eckaus.

"Paul Samuelson transformed everything he touched: the theoretical foundations of his field, the way economics was taught around the world, the ethos and stature of his department, the investment practices of MIT, and the lives of his colleagues and students," said Susan Hockfield, MIT's president, in a statement.