Pete Rozelle, the commissioner who presided over the changes that made the National Football League the premier professional sports organization over the last four decades, died at his home in Rancho Santa Fe, Calif., yesterday. He was 70.

The cause was brain cancer. Mr. Rozelle had a benign brain tumor removed in December 1993.

During Mr. Rozelle's nearly 30 years as commissioner -- which spanned the terms of eight Presidents -- he oversaw a merger and expansion that more than doubled the size of the league, obtained the most lucrative television contract in sports, established Monday night football and introduced revenue-sharing among the teams.

On his watch, the N.F.L. rose to unprecedented heights of popularity, so much so that it surpassed baseball as the national pastime in the eyes of its followers. It also enjoyed huge economic success, attracting escalating television contracts, marketing income and expansion fees.

And his monument to the sport was the Super Bowl.

Soon after the first championship matchup between the well-established N.F.L. and the upstart American Football League in 1967, the game became one of the most watched television programs, garnering ever-higher rights' fees from the networks and escalating prices for tickets, of which there were never enough.

Indeed, when he surprised his employers -- the owners of N.F.L. teams -- by announcing his retirement on March 23, 1989, Mr. Rozelle said the strongest reflection of his tenure was not the merger with the A.F.L., which became final in 1970, or the expansion from 12 to 28 teams. He instead named the annual January game.

''The most fun thing was watching the development of the Super Bowl because the game is what it's all about,'' he said then. ''I really felt a high at every Super Bowl with all the glitz and the spectacular halftime shows.''

When Mr. Rozelle retired later that year, 9 of the 10 television programs with the largest audiences in history were Super Bowls, with No. 1 being the 127 million viewers for Super Bowl XX, between the Chicago Bears and New England Patriots, in 1986. In addition, four polls taken between 1978 and 1985 declared that pro football was America's favorite sport by increasing margins over baseball.

Mr. Rozelle was also consistent in naming the decision he most regretted as commissioner: playing N.F.L. games on Sunday, Nov. 24, 1963, two days after John F. Kennedy was assassinated. He called the decision a mistake even though he had sought advice from Pierre Salinger, the President's press secretary and a friend from Mr. Rozelle's days at the University of San Francisco.

''In the afternoon, I went to the Giants' game,'' Mr. Rozelle said in 1994. ''We had a moment of silence. I could not concentrate on the game. I brooded about my decision the entire game. You have to understand, I was more than depressed over the assassination. I had lost someone whom I'd respected as the leader of our country, but I was also a close friend of the Kennedy family.''

As a leader, Mr. Rozelle blended compromise with showmanship (he was an ever-present figure with an ever-present tan) and was a moderate man with more wit than ego.

His 29-year term as the leader of the N.F.L. came in two parts, the first beginning with his unlikely election on Jan. 26, 1960, at age 33, and including unprecedented success for the league and his C.E.O.-like control of it, along with his reputation as the most skilled head of any pro sports league. The second part of his reign, beginning in the mid-1970's, was less satisfying, with years of turmoil and litigation that led to his resignation.

Afterward, he largely withdrew from the professional sports scene. He is survived by his wife, Carrie; a daughter, Anne Marie, and two grandchildren.

Alvin Ray Rozelle, nicknamed Pete at the age of 5 by an uncle, was born on March 1, 1926, in Los Angeles and grew up in the suburb of Compton. He went to Compton Junior College and, late in World War II, servedon a Navy coastal tanker that, he said, never went far from San Pedro, the southern California port.

Sports were always an interest, if not a passion. He sometimes mentioned that Duke Snider, a high school teammate and later a Hall of Fame baseball player for the Dodgers of Brooklyn and Los Angeles, had knocked out his two front teeth in a basketball practice.

He obtained work as the sports information director at the University of San Francisco, at a salary of $250 a month, when its football and basketball teams were nationally prominent.

A publicity trip before a football game with Fordham at the Randalls Island Stadium in 1951, brought Rozelle to New York for the first time. He was impressed. ''The big time,'' he later said.

Los Angeles was next, as the public relations director for the Rams, the N.F.L. team. After a brief interlude in public relations with a San Francisco firm, he returned to the Rams as general manager.

Bert Bell, who had been a respected N.F.L. commissioner since 1946, died suddenly while attending a Philadelphia Eagles game in October 1959. At a meeting to elect a successor the following January at the Kenilworth Hotel in Miami Beach, the owners of the 12 teams ended a nine-day deadlock by choosing Mr. Rozelle, a compromise candidate, on the 23d ballot.

The new commissioner immediately moved the headquarters from Mr. Bell's Philadelphia to New York and commenced a courtship of television that had far-reaching results.

The first of Mr. Rozelle's several fruitful petitions to Congress brought about legislation legalizing single-network television contracts for professional sports leagues. CBS signed up early in 1961 for an annual fee of $4.65 million to televise the 98 regular-season games. The last such pact of his era, among the three networks in 1987, returned $420 million annually. Such growth affected the value of team franchises which, in Mr. Rozelle's time, went up in transfer deals from $2 million to $80 million.

By initiating the teams' sharing of the revenue from television and with such later innovations as N.F.L. Films and NFL Properties, or contributions to other firsts like N.F.L. Alumni, N.F.L. Charities and the N.F.L. Hall of Fame, Mr. Rozelle put in place the all-for-one, one-for-all concept among the franchises.

He was hardly responsible for the emerging pervasiveness of television. But he did direct its orderly growth with pro football through the eras of blackouts of local teams, Sunday doubleheaders, the Monday night game beginning in 1970 and extended playoffs with wild-card teams.

His first landmark, however, had to do with people, not television. In 1962, he fined George Halas, a league founder and the owner-coach of the Chicago Bears, for abusing field officials. Mr. Halas accepted the fine with some grace and thereafter was one of his strongest supporters.

And because Mr. Rozelle was so shocked by the college basketball gambling scandals of 1951, he set up a security program that was far more advanced than others in sports. In 1963, he fined and suspended two stars, Paul Hornung of the Green Bay Packers and Alex Karras of the Detroit Lions, for placing bets on N.F.L. games. He said it was one of the toughest decisions he ever made.

The suspensions lasted only one season, the fines were minor ($2,000 for each player) and the betting incidents now appear small. But the suspensions were crucial, representing the establishment of his authority and the backing of the owners. ''I felt relieved,'' he said.

But this commissioner had no relief in his attempts to resolve division-of-money issues between the owners and the players union that became heated in the 1970's. The so-called Rozelle rule, which required a team signing a free agent to compensate the player's former team, was declared illegal in a suit brought by John Mackey and other players that eventually cost the league $13.65 million in damages.

In an earlier blow, his policy of ''league think'' -- his mantra promoting unselfishness among the franchises -- was undermined by Al Davis, the maverick owner of the Oakland Raiders, in a 1983 court case that cost the N.F.L. about $50 million.

At the end of that season the Raiders, who had moved to Los Angeles against Mr. Rozelle's wishes, won the Super Bowl. He presented the traditional trophy to Mr. Davis with his congratulations in the customary locker room ceremony on national television.

''That was Pete's finest moment,'' said Ed Sabol, the N.F.L. Films founder. ''He never flinched, while Al never looked him back in the eyes.''

Alvin R Rozelle