First impressions are important. The first impression I had of Sen. Gary Hart of Colorado, a member of the rapidly expanding Democratic presidential field, came in the summer of 1970.

Hart had come to Washington from his Denver law office to set up a campaign headquarters for George McGovern's bid for the Democratic presidential nomination. One hot afternoon, he sat with a semicircle of skeptical reporters, explaining how McGovern would beat the far- ahead favorite for the nomination, Edmund S. Muskie of Maine.

We listened to this unknown, 33-year- old novice campaign manager explain how the lightly regarded McGovern would recruit a new generation of organizers, people who shared his passionate determination to end the Vietnam War, reform the Democratic Party and revive the agenda of John F. Kennedy's New Frontier.

If there was anyone in the room who believed the Hart thesis, he or she did not speak up. The tone of the questioning was relentlessly skeptical. When we were leaving, the thought suddenly crossed my mind: Gary Hart doesn't give a damn whether we believe him or not.

He had made up his mind to join the McGovern campaign for reasons that made sense to him. Whether they made sense to us was a matter of indifference. The briefing was a courtesy to people who would be covering the campaign, nothing more. Two years later, when he and the organization he built had gone out and done exactly what he said they would do, there was no gloating in the triumph at Miami Beach. And when it all turned to dross--in the fiasco of Tom Eagleton's forced withdrawal from the vice presidential nomination--there was no scapegoating from Gary Hart and and no self-exonerating plea for sympathy.

He was, I came to understand, that rarest of political creatures, what sociologist David Riesman would call an inner-directed man. He marched to the beat of his own drummer.

That quality of detachment, of heeding the voice inside his head, not the clamor around him, is what underlies his reputation in the Senate as a loner, a bit aloof, a less-than-persuasive advocate. It is no advantage in a race where people need to be moved, in order to be motivated to work and to vote.

But that kind of inner compass is rare enough in politicians of any age--and particularly among Hart's contemporaries, facing the career-breakthrough pressures of their forties.

It gives me two hunches about the long- shot Hart-for-president campaign. One is that he will likely do what he sets out to do in organizational terms. He readily concedes that there's no issue on the horizon that begins to match the anti-war fervor of 1972, as an organizing tool. But in his stoic fashion, he accepts that, and goes right on to say: we'll still get the organizing done.

When I bumped into him in Oregon during the 1982 campaign, he told me: "I'm sure other candidates (for president) know more of the governors and mayors and party chairmen than I do. But I guarantee you, none of them will know more of the unknown 23-year-old organizers." I believe that.

The second hunch is that the Hart campaign will have a fundamental consistency --a unity that makes it seem whole from beginning to end, whatever that end may be. I am not talking just about staying with the same answer to the same question. I am talking about a steadiness of tone, of purpose and of fundamental outlook.

Hart never talked a lot at the time about what motivated him to work for McGovern (that old reticence). But it was there in the book he wrote about the campaign in 1973, after it was inscribed in history as a colossal failure.

For 20 years, he has believed that America longs to recapture the readiness "for promise, for hope, for excitement" he and others of his age saw in John Kennedy. That hope was killed by assassination, he said, and then twisted out of shape by Vietnam, leaving a legacy of "anger, frustration and alienation."

Muskie, the early favorite in 1972, "failed because he offered nothing new. He offered more solidity and stability, when for ten years people had longed to recapture energy and movement. . . . McGovern's genius was both in correctly reading the longing for change and in realizing the only hope for its success was in a leader who could bridge the national divisions--the generation gap, the racial distrust, the bitterness over the war."

A decade later, Hart is saying the same things. His announcement speech last week said, "We must build a bridge to a new era and master its possibilities. . . . We must once more become a bold, adventurous and pioneering nation."

Hart may misjudge the temper of the nation--and overestimate his own ability to meet its demands, as he did McGovern's. But do not discount a man who follows his own path--and follows it consistently. That in itself is rare.