Washington — Serious, reserved, private. These are not the traits expected of a man running for United States president, but they are the very ones repeatedly assigned to Sen. Gary Hart of Colorado.
''We're taught as Americans to have certain stereotypes about what a politician is,'' says Larry Smith, who spent four years as chief of the Colorado Democrat's staff and now is an administrator at Harvard University's Kennedy School of Government. ''A legislator is seen as one who cajoles, twists arms - all those things we associate with Lyndon Johnson.
''Gary Hart is not that.''
An adviser who spent a year as a congressional fellow in the Hart office offers a similar view. ''His alleged aloofness is an outward manifestation of a man who is admittedly very serious,'' says Coit Blacker, an arms-control expert at Stanford University.
''He tended to be very tough minded during staff meetings, a man of relatively few words,'' Mr. Blacker says. ''My impression was that he made up his mind independently.''
One Democratic staff member who has watched from a distance calls Senator Hart an ''enigma,'' echoing a judgment born partly out of his privateness about his personal life.
Hart has few social buddies in Congress, although Sen. Dale Bumpers (D) of Arkansas is said to be his best senatorial friend.
His penchant for personal privacy is legendary, and it has helped leave several factors in his life unexplained. First, there is his long and rocky marriage to Lee Ludwig, his sweetheart from Bethany College, the Church of the Nazarene school both attended. The couple, who have two children, have twice separated in recent years, and they reunited when he began stumping for president.
Then there is a discrepancy in his birthdate, which is November 28, 1936, but which has been listed in his official biographies as 1937.
And, finally, there are conflicting reports surrounding his name change, during his student career at Yale University, where he attended both divinity and law schools. He, his wife, and his parents shortened their surname from Hartpence to Hart.
Although the move seems an obvious one for a person hoping to be on a ballot some day, Hart has said that he did not push for the change and played little part in it. Yet a Washington Post reporter subsequently searched the court records and found that Hart made the presentation in court.
If the Kansas-born Hart is introverted, it has apparently not kept him from attracting a highly motivated and dedicated staff. In fact, he began his political career as campaign manager for Sen. George McGovern in his 1972 Democratic bid for president by galvanizing young volunteers.
''I think there was not an expectation that he would be (president) but a belief that he should be,'' recalls Mr. Blacker of the Hart staff.
''My strongest impression was that of all the politicians I knew, he was the one I would want to have in the White House,'' he adds.
''He has always had the spark,'' Blacker says. ''There was a certain shyness in public in the past. In private he was never shy.''
For years Hart has been developing detailed positions on major issues of the day.
The question hanging over him was whether he could convey his thinking to the public, an ability that has apparently blossomed only in the past three months.
Alan F. Gordon, who as a reporter for the Rocky Mountain News followed Hart's career closely, remembers that when Hart ran the McGovern campaign and frequently chummed around with actor Warren Beatty, a McGovern backer. ''From the back, with the long hair, you couldn't tell which was which,'' says Mr. Gordon, now of Newsday.
''He looked like he should be more charismatic than he was,'' he says.
But Mr. Gordon recalls one event that foreshadowed the Hart that has swept away voters in New England and surged ahead in recent polls.
It was a dinner in New York to introduce ''new faces'' in the Democratic Party to financial leaders, when the Democrats were trying to recover from the sting of their 1980 defeats.
The crowd heard a succession of Democratic speakers, beginning with Sen. Edward M. Kennedy of Massachusetts and former Vice-President Walter F. Mondale.
The audience ate dinner, grew restless, and began preparing to leave just as the last speaker, Gary Hart, went to the podium. As Hart began to talk, ''people who were putting on hats and coats and shuffling for the exits settled back down in their chairs and paid attention,'' Gordon recalls. ''It was the first time I saw him reach out and make an audience pay attention.''