Allard K. Lowenstein traveled around America carrying a 500-page loose-leaf notebook filled with the names of people he had met in a lifetime of political activism.

Arriving in a new town late at night, as he always seemed to do, he would consult his book, find a local name and make a call: could he have a bed for the night? Usually the reply was enthusiastic, though, often the bed went unused, because often the conversation went on through the night.

Lowenstein was killed Friday in New York, apparently by a sick man who had once been an entry in Lowenstein's notebook, one of the thousands of friends and proteges the lawyer and gadfly collected in his 51 years. In recent months Lowenstein had been worrying about this man, Dennis Sweeney, telling mutual friends that Sweeney was in bad shape and needed help.

At least one of those friends told Lowenstein that there was nothing he could do, to stop worrying about it. But Lowenstein would not let go of the problem, and continued to try to help.Sweeney had an appointment to see Lowenstein in his New York law office Friday afternoon. He kept the appointment, and fired seven shots from a 9 mm semiautomatic pistol into Lowenstein, according to the New York police.

It was a typical situation for Lowenstein, except for the grisly conclusion. He built a life -- a complex, frenetic, exhausting and exhilarating life -- on the people he discovered and pushed into the public arena.

"The most important single contribution he made," political writer Curtis Gans said yesterday, "was as a recruiter of young people into the political process, and then keeping them there. . . He helped make those people believe that idealism was a good thing. I think there's nobody who's doing that now."

Gans was Lowenstein's principal collaborator in 1967, when the two of them organized the dump-Johnson movement, which eventually helped push Lyndon B. Johnson out of the White House. Lowenstein's recruits were the backbone of that movement.

President Carter said Lowenstein's death "cut short a life devoted to reason and justice," and Sen. Edward M. Kennedy (D-Mass.) paid homage to him by calling the Democratic crusader "a one-man demonstration for civil rights."

Lowenstein was a demanding figure, and many of the people he recruited or worked with over the years found it impossible to keep up with him, literally and figuratively. His personal relationships were always intense, but often impermanent. A dozen telephone interviews yesterday with people around the country who knew Lowenstein at various stages of his pilgrimage revealed that many of them had dropped out of Lowenstein's unending parade.

But even those who had falled out with Lowenstein described him yesterday in the awed tones that people reserve for the major figures in their lives. Lowenstein was awesome, in his patience as well as his energy, and always in his determination.

The night Lowenstein's first son was born, Gans recalled yesterday, the expectant father wanted to back out of a commitment to recruit students at a Baltimore meeting of the National Student Congress for the dump-Johnson effort. Gans persuaded him to stick with the schedule, and Lowenstein chose Baltimore over his wife's hospital room in New York.

The success of that dump-Johnson movement gave Lowenstein his greatest measure of fame, but it was not a complete victory for him. Johnson was dumped, but the war in Vietnam, which provoked the movement, went on. This mattered most to Lowenstein, who had an ability to keep issues above personalities, except perhaps his own.

Former senator Eugene McCarthy, whose candidacy in 1968 helped bring down Johnson, recalled yesterday that Lowenstein "was really committed to issues, he didn't care much about personalities."

Lowenstein's interest in issues began when he was a boy growing up in Westchester County in New York. One of his first causes was that of the Spanish Republicans who fought the civil war against Franco's fascists. In later years there were dozens of others, all of them causes Lowenstein saw as struggles for justice and fairness.

"When I was a kid I skipped in grade school," Lowenstein told author Milton Viorst, who writes about him in the new book Fire in the Street, "so I was smaller than the other kids. I wore glasses and I was funny looking. I was picked on and left out a lot. 'Maybe because of that I always identified with ugly girls at dancing school, with blacks in the back of the bus, with anybody that was in some way hurt or excluded. . . ."

Lowenstein grew up comfortably, and attended the Horace Mann School in the Bronx, a private academy for the prosperous. His parents expected him to go to the Ivy League, but Lowenstein picked the University of North Carolina, where he wanted to be, and was, a wrestler. He also became a successful student politician at Chapel Hill, and later was president of the National Student Association, before that organization developed ties to the CIA.

At Chapel Hill, Lowenstein befriended Dr. Frank P. Graham, the University's president, and for two years a U.S. senator. Lowenstein worked for Graham in Washington as an aide, his first direct exposure to Congress and the Washington scene.

After Graham, for whom that son was named, Lowenstein signed on with Eleanor Roosevelt, who became another of his idols. In the 1952 campaign he was national chairman of Students for (Adlai) Stevenson. In 1954 he completed a law degree at Yale, and briefly practiced law from a table in Granson's Restaurant in New York, an establishment his parents bought during the Depression.

After two years in the Army, Lowenstein went to work for Hubert H. Humphrey as a foreign policy aide, a job that took him to southern Africa. In 1959 he left Humphrey and went on a characteristically private mission to the territory of South West Africa (Namibia), sneaking into regions where he was not supposed to be, assembling evidence about South Africa's colonial regime in the territory that he later described in an emotional book, Brutal Mandate.

In 1961 Lowenstein went to Stanford University as an associate dean of men. There he met Dennis Sweeney, the man police say killed him Friday. Sweeney was one of many Stanford students who responded readily to Lowenstein's articulate, forceful advocacy of action on behalf of idealism.

From Stanford he went to North Carolina State University in Raleigh, where he helped organize student civil rights demonstrations, an activism that went down badly with the local populace. In response to the picketing he organized at the Sir Walter Hotel, where members of the North Carolina Legislature hung out, the legislators passed a ban on radical speakers on state campuses. A court later threw out the ban.

The dump-Johnson effort was Lowenstein's first attempt to convert his widening circle of friends and contacts into a political force. During 1967 and 1968 thousands more people were exposed to Lowenstein's energy, and came to know his idiosyncracies: taking his shoes off whenever he could, traveling only at night, preferably late; operating out of phone booths and borrowed guest rooms.

Lowenstein's image of himself seemed to change in 1968. For the first time he decided to put himself forward as a political candidate, intially for the Democratic Senate nomination in New York, the settling for the Democratic Senate nomination in a heavily Republican congressional district on Long Island. With the help of legions of young volunteers, he won that race by a handful of votes, then served a hectic two-year term in the House, specializing in foreign issues and internal change of the institution.

The New York Legislature redistricted the state in 1970, taking Lowenstein's seat away from him. He tried repeatedly to get back to Congress, "a good place for him," in the words of Eugene McCarthy, but the voters in several New York districts refused to cooperate with his ambitions.

Along the way Lowenstein became 40, and then 50 (milestones that astounted his legions of young followers, who seemed to equate Lowenstein's youth with their own), the father of three and then divorced. He accumulated dozens, perhaps hundreds of godchildren, many born to the well-off, well-established young people he liked to befriend as then to provoke into political action that rarely came naturally to them.

What was he looking for in this frantic life? "He was the quintessential politician, really," said an old comrade from the barricades yesterday. "He wanted to create the world in his own image, and run it."