Tom Landry, 75, the founding coach of the Dallas Cowboys who molded the team into a National Football League colossus and in the process helped establish professional football as the nation's premier spectator sport, died yesterday at Baylor University Medical Center in Irving, Tex. He had leukemia.

The medical center issued a news release on behalf of Landry's family, saying, "He will never be forgotten by all of us whose lives he has touched so deeply."

Landry joined the Cowboys as head coach in 1960, when the team was formed, and his arrival coincided with the early years of televised sport as mass spectacle, extending over generational lines and into all regions of the country. Over 29 seasons, he would become a national celebrity by guiding the Cowboys to 19 NFL playoff appearances, 13 division titles, five Super Bowl appearances and two Super Bowl victories. His overall record was 271-180-6.

To millions of TV football fans, he became known as the stony-faced, emotionless figure in the fedora hat, sports jacket and tie, standing with folded arms on the sidelines of every Cowboys game for almost three decades. When the Cowboys had the ball, Landry called all the plays. He devised and dictated the defensive strategy. At all times, he projected an image of order and command. If events on the field of play angered or delighted him, he rarely let it show.

"You can't call a play and make critical decisions if you're emotional," he once said. "When you have to be at your best, you have to be in control."

From the late 1960s through the 1970s and into the 1980s, the Cowboys under Landry were a perennial power in the NFL, with a mystique that transcended the sports community and Texas. They were "America's Team." Such Landry-era players as Roger Staubach, Don Meredith, Randy White, Tony Dorsett, Calvin Hill, Bob Lilly, Don Perkins, Chuck Howley, Mel Renfro and Lee Roy Jordan had national followings. Cowboys fans were found in California, New York and Florida, and there was even a certain cachet attached to the Dallas Cowboys cheerleaders.

Under Landry, the Cowboys revolutionized professional football by computerizing the annual draft of college players, and they instituted a sophisticated training program for the off-season. As an expansion team, they began as a collection of unproven raw recruits and aging veterans long past their athletic primes. But the Cowboys built their team slowly, carefully and patiently. "The one key to success in the NFL is stability," Landry once said. "Get somebody good and stick with him."

On the Cowboys' playing field, the smash-mouth, muscle-and-guts brand of football that had dominated the NFL since the league's inception became increasingly precise, subtle and complex--and under the coach's control. Newsweek magazine columnist Pete Axthelm called it a "mechanical brand of football that is sometimes so efficient it is boring."

But this new development and its architect had a dark side. Some players found Landry cold and aloof. Duane Thomas, the talented and mercurial running back who helped the Cowboys win the 1972 Super Bowl, called Landry "plastic man." A Cowboys wide receiver of the Landry era, Pete Gent, wrote a novel, "North Dallas Forty," which was based loosely on his experiences with the team. The book, which later became a popular movie, described an impersonal football organization whose primary attributes were a lack of compassion, a religious hypocrisy, hard-nosed business dealings and a win-at-all-costs attitude.

That was not how Landry or his friends saw it. Landry, a former president of the Fellowship of Christian Athletes and a lay leader in the United Methodist Church, said he believed there must be more to life than winning at football. "I'm a Christian," he said. "That's the first thing in my life. I want to be the best coach, because that's what I'm doing. . . . I believe winning is important . . . the real danger is when winning becomes the only thing. If you forsake your honesty and integrity to win a football game, it's wrong."

He was a strict disciplinarian, but he was also said to have been deeply concerned about helping players deal with problems related to drug or alcohol abuse, and he hated to have to cut a veteran from the team.

Staubach, the Naval Academy all-American and Heisman Trophy winner who in 1972 was quarterback of the Cowboys' first Super Bowl championship team, said Landry "would give you the shirt off his back if you needed it." In the 1970s, when Staubach underwent shoulder surgery, Landry accompanied his wife to the hospital, and he waited with her outside the operating room until the doctors reported that all was well. Landry, Staubach said, was "the greatest coach in the history of the game."

Tex Schramm, president and general manager of the Cowboys during the Landry years, described the coach as a "great strategist. He knows more about football than anyone else in the world. He doesn't use the psychological or emotional approach. He expects his players to perform each week because they are pros. He's got great intelligence and unlimited confidence in himself."

Landry was a former defensive back with the New York Giants and a coaching assistant during his final playing years. In 1956, he became the Giants' full-time defensive coach, and in that capacity he devised a 4-3 defense that would become standard throughout professional football. That involved replacing an "umbrella" defense--a six-man line with a roving linebacker--with a four-man line and three linebackers. During Landry's four years as the Giants' defensive coach, the team had a record of 33-14-1, with two division titles and an NFL championship. Head coach Jim Lee Howell called Landry "the best defensive coach in the business."

Thomas Wade Landry was born in Mission, Tex., where his father, Ray Landry, operated a garage while also serving as the town's fire chief and superintendent of the Sunday school at First Methodist Church. At Mission High School, the young Landry was an A student, member of the National Honor Society, president of his class and an all-regional fullback on the football team.

He served in the Army Air Forces in World War II and participated in 30 combat missions over Europe with the 8th Air Force. He was co-pilot of a B-17 that crash-landed in France. All nine men aboard walked away from the downed aircraft.

After the war, he enrolled at the University of Texas, where he was quarterback and fullback on the Longhorns football team. In his junior year, he made the all-Southwestern Conference second team. He was co-captain in his senior year. He graduated from Texas in 1949 with a degree in business administration. After taking courses during the next three off-seasons, he received a degree in mechanical engineering from the University of Houston.

After college, he began his professional football career as a cornerback with the old New York Yankees football team in the All-American Football Conference. After the 1949 season, the Yankees merged with the New York Giants of the NFL. For the next six seasons, Landry played cornerback for the Giants. He made the All-Pro defensive team in 1954.

Leaving the Giants in 1960, he considered a head coaching job with the Houston Oilers but opted instead for the Dallas Cowboys. In Landry's first season as head coach, the Cowboys did not win a single game. Not until the 1965 season did the Cowboys win as many games as they lost.

To compensate for the Cowboys' limited football talent in the team's early years, Landry devised a complex and varied offensive game strategy that called for multiple formations, based on the strengths and weaknesses of his own players and the vulnerabilities of his opponents. He was renowned throughout the NFL for his ability to think ahead, not just to the next down but to the next series of downs.

"The trouble with simplistic football," Landry said, "is that if every team concentrates on perfecting routine plays, the best athletes are going to win. If the whole emphasis is on repetition and execution and cutting out mistakes, the game comes down to one thing only--personnel. Well, I reject that as the idea of football. To me, it's a great deal more than just trying to out-personnel the other team."

In a 1968 news release, the NFL described Landry's offense as using "10 or 11 formations a game, with up to six variations of each. This is several times as much offense as the NFL average. . . . The Landry defense, on the other hand, is a one-formation machine. It is as complex as a computer, and its individual parts are coordinated like the works of a clock. There's nothing like it in football. Defense in Dallas is a network of partnerships. On each play at the point of attack, defensive reaction is cooperative by design . . . responsibilities are pre-assigned. Each of the three partners knows the roles of the other two, and all play out their own parts heedless of offensive feints or moves."

During the early years of Landry's leadership, the Cowboys were a typical expansion team. Through the 1964 season, their record was 18-46-4. Nevertheless, he won the confidence of Cowboys owner Clint Murchison, who in 1964 signed him to a 10-year contract. The following year, the Cowboys were 7-7. After that, they were contenders.

They won the NFL's Eastern Division title in both 1966 and 1967, but they lost to the Green Bay Packers each year in the final minutes of the first-round playoff game. They lost division playoff games to the Cleveland Browns in 1968 and 1969. In 1970, they won their first National Football Conference title, but they lost the January 1971 Super Bowl to the Baltimore Colts, 16-13.

In 1966, when the Cowboys made the playoffs for the first time, Landry was the NFL's coach of the year. But he would then undergo five years of intense criticism for failing to win the Big One. Finally, in January 1972, with Staubach as quarterback and Duane Thomas and Calvin Hill as running backs, the Cowboys won their first Super Bowl, beating the Miami Dolphins, 24-3.

They did not return the following season. On Dec. 31, 1972, at RFK Stadium in Washington, the Cowboys lost the NFC title game 26-3 to Coach George Allen's Redskins, who in January 1973 would be defeated in the Super Bowl by the Miami Dolphins. During the 1970s and 1980s, the Cowboys-Redskins rivalry would be one of the most intense in the NFL. At the end of the strike-shortened 1982 season, the two teams would meet once again in the NFC title game, which the Redskins won 31-17. They went on to defeat the Dolphins in the 1983 Super Bowl, 27-17.

Under Landry, the Cowboys would return to the Super Bowl three times after their 1972 victory, beating the Denver Broncos, 27-10, in 1978, and losing to the Pittsburgh Steelers in 1976 and 1979.

By dint of the Cowboys' success on the field and his own longevity as head coach, Landry had long since become a national celebrity by the mid-1970s, and the Redskins-Cowboys rivalry was common knowledge across the country. Both were featured in a 1983 American Express television commercial. The advertisement showed Landry riding into town, then walking into a tavern, where he was immediately surrounded by strong, large men in burgundy and gold football uniforms. "Don't you know me? I'm one of the most famous cowboys in Texas," Landry said in the commercial. "People don't always recognize me without this 10-gallon hat. That's why I always carry this American Express card. It sure comes in handy if you're surrounded by Redskins."

But by the early 1980s, the Cowboys' star had lost some of its luster. Owner Murchison's health started to decline, and he was losing money in the collapse of the Texas real estate and oil markets. He sold the Cowboys to an 11-member consortium headed by H.R. "Bum" Bright for $86 million. Bright never meddled with on-field football operations, but the Cowboys' fortunes took a dive.

For 20 consecutive seasons, since 1966, the Cowboys had enjoyed a winning record. During the five years of the Bright group ownership, they were 36-44 and did not win a playoff game. In 1988, Landry's last season as head coach, the Cowboys won three games and lost 13. In early 1989, the Cowboys were sold to Jerry Jones, a former football player at the University of Arkansas who had made a fortune in insurance, gas and oil. Jones paid an estimated $140 million for the Cowboys. One of his first acts was to fire Landry and Schramm, the Cowboys' longtime general manager.

"You've taken my team away from me," said a stunned and disbelieving Landry at the time. But he would later declare that he was not bitter and say that he got out of professional football at what for him was the right time.

"When I moved out, I found it very enjoyable," he later told the Dallas Morning News. "I started getting into different projects, and my mind wasn't on the Cowboys or football. I had no feelings one way or the other. I had run my course. I was fortunate. The good Lord probably took that away from me and put me in another category. I got a different outlook."

After leaving the Cowboys, Landry was a partner with his son in an investment company, and he served as a goodwill ambassador for the Fellowship of Christian Athletes, attending golf tournaments, breakfasts, lunches and dinners.

In 1993, he returned to Texas Stadium for a ceremony marking his induction to the Ring of Honor, which the Cowboys established in 1975 to honor players who had made outstanding contributions to the team.

Survivors include his wife, the former Alicia Wiggs, whom he had met in college and married in 1949; his son, Tom Jr.; and his daughter, Kitty Phillips.