Kenneth P. O'Donnell, John F. Kennedy's closest aide in the White House, is dead at 53. He died early yesterday at Beth Israel Hospital in Boston, where he had been admitted in critical condition on Aug. 11. His family asked his doctors not to discuss the details of his illness, but it is known he was suffering from an [WORD ILLEGIBLE] and a liver ailment.

O'Donnell was listed officially as President Kennedy's appointments secretary during the White House years, but he was much more than the guardian of the President's gate. He was perhaps the most trusted and influential of that tightly knit band around the President.

O'Donnell had a hand in virtually every crisis in the Kennedy White House, from the Bay of Pigs to the Cuban missile confrontation. He knew all the secrets, personal and political, and typically kept them all to himself.

What gave O'Donnell his special role was his intimacy with both of the Kennedy brothers, John and Robert. He had been Bob Kennedy's roommate and friend at Harvard; it was Bob who brought him into his brother's political orbit in 1946.

Over the years, he became almost the perfect aide, tight-lipped, self-efficing shrewd, tough, totally loyal, and never hesitant to say exactly what he thought. He had in that sense, the most valuable asset of a presidential adviser - like Harry Hopkins under Franklin Roosevelt, he dared to say no to the President's face.

The press, is trying to assess his rude, dubbed him as one of the "Irish Hafia," a foolish term that persists in describing close presidential counselors. From O'Donnell's day we have gone on to the "Texas Mafia," the "Southern California Mafia" and now the "Georgia Mafia." Whatever, O'Tonnell was one of the few who held an extraordinarily influential position in the shadows of presidential power.

It was typical of O'Donnell to shun the spotlight. Ad he once said about himself when he was trying unsuccessfully to launch his own political career. "They (the public) don't know me personally. They know who I am."

That was true. Mary McGrory, who knows the Boston breed of politician as well as anyone, once described O'Donnell as having the reputation of being the most uncommunicative public official in Washington since Calvin Coolige.

"His general mode of address was out of the corner of the mouth," she wrote, "in the manner of an Irish volunteer during the Troubles, passing the word to his comrades."

In private, though, when surrounded by the Kennedy brothers and other key counselors, O'Donnell could be refreshingly blunt. A flavor of his style comes through in the book O'Donnell and another old Jack Kennedy crony, Dave Powers, wrote about their memories of JFK.

Kenny O'Donnell, on describing his first impression of John Kennedy:

"There were very few people in 1946 who really thought of him as a presidential possibility, outside of his father and his grandfather and a few admiring Boston Irish mothers. When I first met him that year, I did not think that he would even be elected to the House of Representatives.

"Bobby Kennedy, by closest friend in the locker room at Harvard, brought me to Jack's rooms at the Bellevue Hotel one afternoon after spring football pratice, and introduced me to him. He seemed too boyish and shy to be running against experienced politicians like Mike Neville and John Cotter in that tough congressional district. Later, when Bobby asked me if I would do some work for Jack in Cambridge, I said to him, 'I'll do it as a favor for you, but he'll never make it.' I was still not particularly impressed by him when he did make it to Congress.

"Like many young war veterans of my age in Massachusetts who were interested in the political situation, I did not begin to pay much attention to Jack Kennedy as a congressman until he refused to sign a petition for a presidential pardon for James M. Curley and attacked the American Legion for its opposition to low-cost public housing projects."

Kenny O'Donnell was a man of few words who did not tolerate bombast or sham easily. Mike Barnicle of The Boston Globe captured the essence of him in a tribute yesterday. It was O'Donnell who kept slugging away at life, as Barnicle put it, while so many others cashed in on their years and exalted roles in that supposedly splendid Kennedy "Camelot."

"I got to laugh at all these guys who talk about working in the White House, and what a tough job it is, all the hours and everything." Barnicle qotes O'Donnell as saying "Tough job my ass. It was the best job I ever had."

Like Kennedy, O'Donnell was a World War II veteran and genuine hero, as that now seemingly old-fashioned term was employed then. He flew 30 missions as a bombardier in a B-17 squadron before he was shot down over Belgium. He was imprisoned, escaped, and emerged with the Distinguished Flying Cross and Air Medal with Four Oak Leaf Clusters.

After the war, O'Donnell entered Harvard on a scholarship, where he distinguished himself academically and as an athlete. He was a slim, wiry man, much like Bob Kennedy, who made up for any lack of size and natural skill in determined aggressiveness.

O'Donnell and Bob Kennedy were teammates on the Harvard football team for three seasons, beginning in 1946. He closed out his football career, after having been named team captain, in dramatic fashion: he scored the winning touchdown in his last game, against arch-rival Yale, while maneuvering on a broken leg.

After graduating with honors, he entered private industry, working mainly as a public relations consultant while at the same time attending the Boston College of Law. But even then Kenny O'Donnell's fate was linked inseparably with that of the Kennedys. In 1952, when John Kennedy ran for an won a seat in the Senate, Bob Kennedy managed his brother's campaign, assisted by O'Donnell as chief lieutenant. The pattern had been established.

Five years later, when Bob Kennedy was counsel to the Senate Rackets Committee, he once again called on his old friend to assist him. O'Donnell answered the call immediately.

When asked why he had left his seashore hoe in Winthrop, Mass., to come to Washington in the sweltering summertime, O'Donnell replied with characteristic understatement:

"Bobby wanted me to take over some of his burden, and he said I'd like the work."

From that point on, Kenny O'Donnell's life was bound to the Kennedy brothers political odyssey. He handled with the problems as they arose, and proved himself to be indispensable.

O'Donnell rode the Kennedy comet from beginning to end. It's probably not too much to suggest that when their lights went out something within O'Donnell died, too.

He was in Dallas on the day of that first Kennedy assassination; in fact, he had arranged the trip. As the motorcade wound its way into Dealey Plaza, and history, O'Donnell was riding along scarely 10 feet behind the President's car. He had just noted the time, and was pleased that the caravan was only five minutes behind schedule, when the shots rang out. His friend, Dave Powers, turned oand said, "Kenny, I think the President's been shot."

O'Donnell later described the scene in his and Powers' book, "Johnny, We Hardly Knew Ye":

"I made a quick sign of the cross and said, 'What makes you think that)'

"Look at him!" Dave said. "He was over on the right, with his arm stretched out. Now he's slumped over toward Jackie, holding his throat.'

"While we both stared at the President, the third shot took the side of his head off. We saw pieces of bone and brain tissue and bits of his reddish hair flying though the air. The impact lifted him and shook him limply, as if he was a rag doll, and then he dropped out of our sight, sprawled across the back seat of the car. I said to Dave, 'He's dead.'"

O'Donnell stayed on in the Whie House at Lyndon Johnson's request, but as everyone knew, his heart wasn't in it. When Bob Kennedy challenged the President directly in 1968, in that fateful year that so tore at the country and the Democratic Party, O'Donnell inevitably became his campaign manager. And once again he was a witness to another Kennedy assassination.

In his own right, O'Donnell had attempted a political career in Massachusetts. Twice, in 1966 and again in 1970, he sought the Democratic nomination for governor. The first time he had the help of Bob Kennedy, who campaigned on his behalf by saying:

"There wasn't a major decision that was made by President Kennedy that Kenny O'Donnell did not share in."

But O'Donnell was not an effective candidate. His political gifts were in counseling, not campaigning.

In recent years, O'Donnell continued to dabble at politics -assisting Hubert Humphrey in 1972, and talking of running again himself - but his main occupation was in a public relations and management consulting service he ran from an office in Boston's Park Square Building.

He also was deeply involved in the work of the Kennedy Library Foundation. To the end, he was a keeper of the Kennedy flame even at a time when political currents were running in other directions.

Philip Kenneth O'Donnell, as he was christened, was born in Worcester, Mass., March 24, 1924, the son of Cleo O'Donnell, a well known Holy Cross coach and athletic director.

Later, O'Donnell changed the order of his name to Kenneth P. He and his first wife, Helen, had five children, three sons and two daughters: Kenneth P. Jr., Kevin M., Mark F., Kathleen Schlichenmaier,and Helen O'Donnell.

Mrs. O'Donnell died last January at the age of 50, not long after returning to work as a clerk for the Massachusetts Supreme Court, a post she had held before the O'Donnells moved to Washington with President Kennedy.

On April 30, O'Donnell remarried in the Harvard Memorial Church. His second wife, Asta Hanna Helga Steinfutt, is a German national who has been a physical education teacher in New York and Cambridge.

Funeral arrangements were not complete last night.