David E. Lilienthal, 81, a driving, determined lawyer who helped bring cheap electricity to the middle South as head of the Tennessee Valley Authority and who later helped bring the nation into the nuclear age as the first head of the Atomic Energy Commission, died Wednesday in New York City.

Throughout his govenment career, Mr. Lilienthal distinguished himself as a forceful fighter for his beliefs and philosophies, which occasionally seemed paradoxical and at variance with what might have been expected of a man at the top of two of the most important government organizations of his time.

As chairman of TVA from 1941 to 1946, he presided over the nation's largest electric power system. But Mr. Lilienthal became known as an articulate and outspoken enemy of "big government" and as a man who viewed "overcentralized administration [as] a hazard to democracy and freedom."

And as the head of the nation's atomic program in the years shortly after the explosion of the first atom bombs, Mr. Lilienthal stood against the rigid bureaucratic restriction and obsessive concern with secrecy that characterized the period. It was his frequently expressed wish that the power of the atom should be brought as soon as feasible into the everyday lives and thoughts of the nation's people.

Such positions, no less than his skill and vigor in championing them, made him a lightning rod for controversy, which seemed to swirl about him throughout a career that was filled with achievement and accomplishment.

Mr. Lilienthal died at the Sheraton Centre after going to New York from his home in Princeton, N.J., for a doctor's appointment. His death was attributed to a heart attack.

A native of Morton, Ill., Mr. Lilienthal became an amateur boxer, which helped inculcate in him as a young man the resilient tenacity that characterized him later.

At DePauw University in Greencastle, Ind., where Mr. Lilienthal received his bachelor's degree in 1920, he earned both a Phi Beta Kappa key and a reputation as a light-heavyweight boxer.

He told of an early experience with a professional known as the Tacoma Tiger who, Mr. Lilienthal said, "damn near killed me," but who "taught me something about coming up off the floor and taking more -- which has come in handy."

After obtaining his law degree at Harvard in 1923, Mr. Lilienthal began the practice of public utility law that eventually led him to TVA. Among the building blocks of his reputation was his work as special counsel for the city of Chicago in a landmark telephone rate controversy that resulted in a decision by the U.S. Supreme Court, ordering a $20 million refund to telephone subscribers. While practicing, he was a prolific contributor of articles to journals of law and public affairs.

Although his abilities were beyond dispute, as Mr. Lilienthal told the story it was chance that determined the time and circumstances of his entry into public service.

One afternoon, he said, he happened to remain at his desk rather than keep a date to play handball.

The telephone rang. It was Philip LaFollette, the governor of Wisconsin, with an invitation to join the state's public service commission.

"If I had gone to the gym that afternoon," Mr. Lilienthal later spculated, "I would have missed the phone call from Phil LaFollette, and I doubt if he would have called again."

The Wisconsin post led to the appointment of Mr. Lilienthal at the age of 33 -- and at the outset of Franklin D. Roosevelt's New Deal -- as a member of TVA's three-man board of directors.

Mr. Lilienthal became known as the driving force behind FDR's regional development program. With his philosophy that electricity was "the people's business," it fell to Mr. Lilienthal ot direct TVA's vast project for developing power as well as sending electricity to cities and towns, industries and farm cooperatives throughout the Tennessee Valley.

A self-described "craftsman in public affairs," Mr. Lilienthal reveled in the opportunity to put into practice his belief that "electricity is not just a coomodity to be bought like groceries or automobiles. To most people it is a symbol, a symbol of freedom from drudgery, a symbol of a new way of living. . . As much as any other single force, electricity can help us to eliminate the sweatshop and the slum. It can help us to restore a balance of opportunity between city and country -- between the factory and farm."

As much a visionary as any man to occupy a position of such high responsibility, Mr. Lilienthal received the modest salary of $10,000 a year to serve as chairman of the billion-dollar enterprise and spurned opportunities to move elsewhere at higher pay.

He had, he explained "made a lot of money [as a lawyer] and found out how boring it could be. I realized I'd wake up some day with the best years of my life gone and find I'd done nothing I had really enjoyed."

Roosevelt named Mr. Lilienthal to a full nine-year term as TVA director in 1936, and on Sept. 15, 1941, appointed him chairman. President Truman reappointed him in 1945 for another nine-year term.

While with TVA, Mr. Lilienthal survived controversies and clashes with the private utilities and with Tennessee senator Kenneth D. McKellar, the crusty chairman of the Appropriations Committee who had tried periodically to curb the project's independence. Inevitabley, Mr. Lilienthal acquired enough antagonists to insure opposition to his Oct. 28, 1946, appointment to head the Atomic Engery Commission, the giant civilian agency created to take over from the Army and run the nation's new-born nuclear program.

Contentious and argumentative hearings were held. McKellar seized the opportunity to harass and calcuminate his old foe and ultimately to charge him with harboring an affinity for communism.

"Your sympathies are very leftist, are they not?" McKellar demanded.

Without text or preparation, Mr. Lilienthal launched into an emotional assertion of his personal belief in democracy. One of its tenets, he asserted, was a "repugnance to anyone who would steal from a human being that which is most precious to him, his good name be imputing things to him, by innuendo, or by insinuation."

"I deeply believe," he continued, in the capacity of democracy to surmount any trials that may lie ahead provided only we practice it in our daily lives."

The speech was a triumph.

Confirmed as AEC chairman, Mr. Lilienthal went on to head the agency as it set up new laboratories to explore atomic development, promoted research into peaceful uses of the atom and at the same time refined and improved the nation's nuclear weapons capability, stockpiling an ever-increasing supply of mass-produced bombs.

Few questions of science or public policy aroused so much passion and partisanship as did the development of atomic energy at the end of World War II and the start of the cold war, the period of Mr. Lilienthal's stewardship.

Zealously eager to see atomic energy harnessed for peaceful purposes, Mr. Lilienthal was associated before going to the AEC with a proposal to place under international control all dangerous operations involving atomic energy.

During his term as chairman, it was discovered that the United States no longer held a nuclear monopoly. Behind-the-scenes debate raged over the troubling question of whether to build the hydrogen bomb. Initially at least, Mr. Lilienthal was against it.

Early in 1950, not long after acrimonious hearings were spearheaded by a senator who accused him of mismanagement, Mr. Lilienthal resigned, ending 19 years of public service.

"Taking command of a decaying wartime enterprise in 1946, he had built it into an effective, modern institution of government," wrote Richard G. Hewlett and Francis Duncan in their 1969 history of the AEC. Idealistic, energetic, eager for challenge, although also impatient with detail and emotional in his reactions to events, the authors said, Mr. Lilienthal had "given America some sense of the promise of atomic energy, something to displace the grim spector of Hiroshima."

After leaving government he established a corporation to provide managerial and technical services to developing nations.

One of his post-Washington activities was an effort, made at the behest of the then shah of Iran to turn a desert in the southwest of that country into a replica of the TVA.

He also spoke out frequently and wrote often on public issues.

Survivors include his wife, Helen, a son and a daughter, five grandchildren and three great-grandchildren.