William F. Buckley described him as the original activist of our times. Sen. Edward M. Kennedy, another of the speakers at a memorial service for Allard K. Lowenstein today, said: "For me and for so many others, he was our brother."

Lowenstein, slain Friday in his law office by a man he had once recruited to register black voters in Mississippi, had kindled concerns for peace and justice in many Americans. More than 3,000 of those he had helped, inspired and loved today crowded the Central Synagogue and the streets outside to listen once more to his words and think yet again of his dreams.

Kennedy took note of Lowenstein's extraordinary range of friends, as evident in the audience as among the speakers. "Who but Al could have as friends Bill Buckley and Bobby Kennedy" he asked.

Buckley wondered aloud, as many of Lowenstein's friends had wondered before, "How did he live such a life, so hectic with public concern?"

"Al always set aside time for his family," his nephew, Douglas Lowenstein, said of the man whose energy had exhausted his friends on many long trips and late nights in the service of many causes.Then he drew laughter with his explanation: "Unfortunately for us, it was usually between midnight and three a.m."

The memorial for Lowenstein mingled laughter over good days with wrenching memories and tears.

People spoke of the rumpled suits, the chronic lateness, the inexhaustible energy that were hallmarks of the man Indiana Congressman Andrew Jacobs called "a gentle tornado."

The service also resonated with memories of others cut down in our time.

Lowenstein wrote two years ago on the 10th anniversary of the assassination of Robert F. Kennedy: "We have learned that America is not as innocent nor as easily changed as we once thought."

But his message then, which David Saperstein read again today, was not despair in the face of difficulties, but a call for new effort.

"It is past time to dream again of making things better . . . it is past times to weave a tapestry of peace and freedom for all the people of the world," he wrote.

Lowenstein's nephew and Jacobs both quoted from a speech Robert Kennedy gave to South African students in Cape Town in 1966. "Let no one be discouraged by the belief that there is nothing one man or one woman can do," Kennedy said, because "from numberless diverse acts of human courage the history of man is written."

The faces in today's crowd were a good deal older than in the 1960s when they joined Lowenstein in Mississippi to work for civil rights, or in New Hampshire to seek an end to the Vietnam war, but speaker after speaker urged them not to grow discouraged and abandon their efforts to further the goals they shared with Lowenstein.

Rep. Pete McCloskey (R-Calif.) recalled that Lowenstein once asked him, "How many great leaders do we have to lose to a deranged person with a concealed weapon?" and pledged that he would take from Lowenstein's death a new commitment to bring about laws controlling the sale of handguns.

The challenge for all Lowenstein's friends, Buckley said, was to fill the vacuum left by his death.

Lowenstein's former wife, Jenny Littlefield, and their three children sat with other family members in two front pews during the 90-minute service that alternated speeches with some of Lowenstein's favorite folk songs.

Peter Yarrow, later joined by Mary Travers, two-thirds of the folksinging group Peter, Paul and Mary, sang "Stewball" and the spiritual "Amazing Grace."

The congregation joined in -- as many of them had with Lowenstein in many parts of the country. "There was no place he wouldn't go and no discomfort he wouldn't bear," Jacobs said of him.

Former ambassador to the United Nations Andrew Young said Lowenstein was a part of a "moment of conscience" that came to the United States in the 1960s. His actions exemplified what the Old Testament prophets might have done had they lived in his time, Young said.

Those who came to pay tribute to Lowenstein also included New York Gov. Hugh Carey, Mayor Ed Koch, Jacqueline Onassis, Robert Kennedy Jr., Coretta Scott King and former New York mayor John V. Lindsay.

"What a friend we have all lost," Sen. Kennedy said.

As Yarrow and Travers sang "Weave me the sunshine out of the falling rain. Weave me the hope of a new tomorrow," Lowenstein's pallbearers wheeled his oak coffin out of the synagogue and his friends filed slowly out to contemplate that never again will they get an improbable call at an unlikely time from someone who introduces himself and says: "Al Lowenstein told me to call this number."