Stewart Udall, an advocate for the American West who oversaw the addition of 2.4 million acres to national parks and pushed for landmark environmental legislation as U.S. Interior secretary under presidents John F. Kennedy and Lyndon B. Johnson, has died. He was 90.

Mr. Udall died Saturday at his home in Santa Fe, N.M., of natural causes, according to an e-mailed statement from Marissa Padilla, press secretary to U.S. Sen. Thomas Udall, Stewart's son. He had been confined to his bed following a fall last week, the statement said.

"He was a square shooter and he was a very outspoken man," Willard Wirtz, the secretary of Labor under Kennedy and the last surviving Kennedy cabinet member, said in a telephone interview Saturday.

"We always agreed on almost everything," said Mr. Wirtz, now 98, adding that he last talked to Mr. Udall on the telephone about a year ago.

A congressman from Arizona before joining Kennedy's administration, Mr. Udall was part of a famous Democratic family. His brother, Morris, known as Mo, succeeded him in the U.S. House and unsuccessfully sought the Democratic nomination for president in 1976. Morris's son, Mark, is a senator from Colorado. Stewart's son, Tom, is a senator from New Mexico.

"The country is lucky that, while the elder Udall generation has passed from the scene, they are today being followed by two United States Senators, the same family and the same values," said Rep. David Obey, the chairman of the House Appropriations Committee. Mr. Obey, D-Wis., called Mr. Udall "a great man."

During eight years heading the Interior Department, from 1961 to 1969, Mr. Udall crusaded for the Clean Air Act, the Wilderness Act, the Land and Water Conservation Fund Act and the Wild and Scenic Rivers Act.

The National Park Service, created in 1916, was expanded under Mr. Udall to include four new national parks, six new national monuments, eight seashores and lakeshores, nine recreation areas, 20 historic sites and 56 wildlife refuges, according to a biography compiled by the University of Arizona Library.

Mr. Udall was "one of the greatest champions in our nation's history for conservation," House Speaker Nancy Pelosi said in an e-mailed statement. As Interior secretary he "championed the burgeoning environmental movement, protected the treasures that are our parks, seashores and wildlife refuges, worked for energy independence, and ensured the arts remain a central part of civic life," Ms.Pelosi, D-Calif., said.

He was the first Cabinet member named by Kennedy in 1961, and the youngest. As a congressman, he had been influential in persuading his state's Democrats to support Kennedy during the 1960 Democratic National Convention.

In office, Mr. Udall set three top goals, according to a 1962 profile in BusinessWeek: protect the future of Indians and Alaskan Eskimos, assert greater federal control over the allocation of water resources and confront the country's scarcity of sheltered land. BusinessWeek called him "the Kennedy administration's peripatetic apostle of outdoor life."

Increased travel on American highways and railroads had inundated park rangers with an influx of visitors, Mr. Udall told Atlantic Monthly in 1961. Five years earlier, Congress had passed Mission 66, a 10-year rehabilitation plan to accommodate the overflow of hikers and campers. Mr. Udall told Atlantic Monthly that during his tenure, "special care will be taken that in the planning of roads, buildings, and village developments, nature will take precedence over the needs of the modern man."

Mr. Udall persuaded Kennedy to call a White House meeting on conservation, the first since Theodore Roosevelt's presidency. "Recreation and fish and wildlife will finally be given a seat at the head table in the federal government," Mr. Udall told BusinessWeek.

Stewart Lee Udall was born on Jan. 31, 1920, in St. Johns, Arizona, a territory near the New Mexico border once belonging to the Apache and Navajo Indians.

His parents, Levi and Louise, were descendants of 19th century Mormon pioneers. His paternal grandfather, a bishop in the Mormon church, had come to St. Johns to expand it as a Mormon settlement starting in 1880.

Mr. Udall's interest in public office originated with his father, who taught himself law and sat as a county court judge for 15 years in St. Johns until winning election to the Arizona Supreme Court in 1947. He served two stints as chief justice.

"I was taught that a person may aspire to nothing higher than to be a public servant," Stewart Udall told the Saturday Evening Post in 1961.

Mr. Udall attended Eastern Arizona (formerly Gila) Junior College in 1937, transferring to the University of Arizona in 1938. As expected of a Mormon son, he dedicated two years to an evangelical mission in 1940 to New York and Pennsylvania before traveling to Europe and joining the U.S. Air Force as a B-24 tail gunner during World War II.

After the war, he returned to school and played for the University of Arizona's first basketball team in 1946. He graduated in 1948 with a law degree and, two years later, opened a firm with brother Mo in Tucson.

He won election to the U.S. House as a Democrat in 1954 and served until his appointment as Interior secretary in January 1961.

After leaving government service in 1969, Mr. Udall taught for a year at Yale University's School of Forestry as a visiting professor of environmental humanism. He advocated the use of solar energy to remedy the 1970s energy crisis. He pressed the courts and Congress on behalf of uranium miners who had helped build the U.S. nuclear arsenal, winning passage of the Radiation Exposure and Compensation Act in 1990.

Mr. Udall married Ermalee Webb in 1948, and they had six children. Son Tom served five terms in the House before winning his Senate seat in 2008.

Mr. Udall wrote books and articles on the environment and practiced law.

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