Lawrence F. O'Brien, who died last week of cancer, was many things: a key figure in John F. Kennedy's "Irish Mafia," an architect of Lyndon Johnson's Great Society legislation, a Cabinet member, the target of the Watergate break-in that eventually cost Richard Nixon the presidency and, later in life, a most successful commissioner of the National Basketball Association.

But above all else, Larry O'Brien was a Democrat -- a politician devoted to the nurture of his party. To salute him and his work is to defend what is now most denigrated in American politics: the principle that parties matter, even more than personal ambitions or the policy clashes of the moment.

The son of immigrants from County Cork who ran a rooming house and restaurant in Springfield, Mass., he was different from the others in the Kennedy circle -- and not just because he had no enthusiasm for touch football. O'Brien had been actively involved in Democratic politics before JFK came along, and he stayed involved long after he was gone.

Devoted as he was to President Kennedy and to his brother Robert Kennedy, it was perfectly in character for O'Brien to give generously of his talents to President Johnson and to Hubert Humphrey, when they carried the Democratic banner after the deaths of the Kennedy brothers.

Some Kennedy courtiers never forgave O'Brien for that. But anyone who understood him knew that his concept of loyalty went well beyond the individual to an institution he genuinely believed served the interests of most Americans -- the Democratic Party.

I met O'Brien during the West Virginia primary of 1960. We hooked up one day at the Kennedy headquarters in the basement of the Kanawha Hotel in Charleston, where he and Matt Reese and Bob McDonough worked the phones 18 hours a day, and drove together down to Beckley. By the end of the drive, I'd not only had a lesson in O'Brien's techniques for political organizing but an insight into the values that framed his life.

He was a small-d democrat as well as a Democrat. He believed that the people could and should rule. But unlike so many of the current crop of self-proclaimed "populists," who visualize themselves as personal embodiments of the mass will, O'Brien understood that popular rule required mobilization. And mobilization required political party organization.

The secret of his success as a political organizer was no secret at all; he laid it out in simple terms in the "O'Brien Manual." It is all about participation, about techniques for expanding the campaign from the cadre of insiders to wider and wider circles of volunteers; of reaching people at the doorstep and giving them a sense of involvement in a candidacy.

My dog-eared copy reads: "Volunteers are essential to the success of any political campaign. . . . There is no such thing as having a surplus of volunteers. . . . There is always work to be done in a political campaign."

It is no accident that the campaigns he helped design in the 1960s saw levels of turnout the Democrats have not been able to match ever since.

His techniques as a congressional liaison for Kennedy and Johnson rested on the same principle -- finding ways to involve members of Congress enough in the framing of a program that they acquired a sense of ownership in seeing it passed. It wasn't easy, for Kennedy had too few allies on Capitol Hill and Johnson had almost too much ego to let others play. But O'Brien did the job with skill, in large part because he never let himself become a cynic.

"I always felt," he wrote, "that we could never discount any member of Congress, no matter how much we might disagree with him. The people of his state or his district had elected him; he spoke for them and he was, therefore, deserving of our respect."

O'Brien understood that the goal of politics was not just to win but to govern. The policy issue that concerned him most, always, was education. He knew, as well as Mr. Jefferson, that democracy without education was a contradiction in terms. I don't believe I had any interview with him during the Kennedy years that he did not express his frustration at the lack of votes to pass a federal aid-to-education bill. I know he was never happier than when Johnson signed the landmark education bills of his presidency.

But the job O'Brien valued most was the chairmanship of the Democratic National Committee, though the two times he held it between 1968 and 1972 were hard times for his party. "I'm proud to be known as a politician," he wrote in his memoirs. "Politics is the art of the possible, and it is an intensely personal art."

O'Brien practiced that art as well as anyone Washington has seen in a long, long time. He titled his book "No Final Victories," because he was always a realist. But his final victory was sustaining the Democratic Party -- both in government and at the grass roots -- at a time when that was tough to do.