THE ALDERMEN and ward heelers of Chicago gathered over cocktails in a Loop boardroom to hear from Sen. Gary Hart, whose presence they had not felt for years.

"You people are the backbone of this country," Hart began hopefully. "You don't need cowboys from Colorado to tell you how to do politics. Most of you have forgotten more politics than I'll ever know."

But in the rear of the room, it was clear that they have not forgotten as much as Hart might like.

"You say 'Gary Hart' to the people in this room," observed state Sen. Phil Rock, the Illinois Democratic chairman, "and, if they know anything about him, what they know is that he's the guy who was the campaign manager who threw them out of the '72 convention.

"That's what they know about Gary Hart!"

Yet this is no longer that Gary Hart -- and has not been for some time. He is today a two-term Democratic senator who won reelection in the Republican-dominated West in the midst of the 1980 Reagan sweep, and who is now trying to manage his own way to the presidency.

In so doing, Hart, like his party, has been preoccupied with carving a new identity and promoting new ways of doing things. This is not an assertion of personal newness as in the "New Nixon" of 1968. Instead, Hart has worked the country for two years, seeking to lay his own new foundation for issues and politics.

Let Walter Mondale and Alan Cranston and Edward Kennedy aid the 1982 congressional candidates by contributing greenbacks by the thousands; Hart aided them by contributing white papers by the dozens, outlining new positions on old issues or at least new ways of addressing old issues.

For Hart, the emphasis is all on matters of substance and all things new. He talks of 1984 as the year of a "new generation," for which he aspires to be a spokesman.

He pledges "new ideas" and a "new, issues-oriented" campaign style, built around a roadshow of issues seminars, not just the standard fare of speeches. He envisions "new ways of communicating," as an adviser puts it, among them using cable and satellite television to carry his new ideas seminars and roundtables to the nation.

He parades all this newness under a banner of "neo-liberalism," a star spangler that he did not originate, does not like and cannot quite define -- but which is at the head of his parade nonetheless, courtesy of the political lexicographers who are taking his measure.

"The Democratic Party cannot be the party that just recommends defense cuts," Hart told another gathering of Chicagoans, illustrating that the new philosophy comes complete with old-fashioned pragmatism. "If we do, we will lose election after election after election. I say that to you as progressive Democrats. But I mean it."

His audience this time was composed largely of people who like their politics liberal -- and who liked Gary Hart's politics way back when he was helping to throw Richard J. Daley out of that 1972 convention, in the name of George McGovern and liberalism and opposition to the Vietnam war. They were assembled in the apartment of a former ambassador to Norway, Louis Lerner.

Hart gave them the bare bones of what life in one neo-liberal's presidency would be like. He is tall and slim, like a teenager who has not yet filled out the full capacity of his frame. His face could easily be that of the 45-year-old man that he in fact is, but his coiffure is that of one 20 years younger. He seems from a distance more like a Senate aide than a senator, more like a presidential campaign manager than a presidential candidate.

He also is shy; he has had to force himself to learn to campaign. But he has not had to force himself to delve deeply into issues in search of alternatives -- that is both his inclination and his strength. In the small confines of the Lerner apartment, Hart was at his best, talking presidential priorities.

"Between the election and my inauguration, I would draft an arms control agreement," said Hart, an advocate of a mutually verifiable nuclear freeze. "I would contact the leader of the Soviets and challenge him to do the same, and I would ask him to meet me in Geneva and to put it on the table. . . . We don't have a forceful effort to negotiate arms agreement now, because the president does not believe in it. You've got a bunch of people here (in power in Washington) who don't believe in arms control agreements -- and it's a scary proposition . . .

"Second, once in the Oval Office, I would convene a meeting of the auto industry, and the union leaders and leading bankers, and I would put before them a contract . . ."

He would jawbone all sides, invoking the national interest, hoping for the sort of long-term commitments for capital, and investment, and plant modernization and job retraining that would get America moving again, "and if that were successful, I would do the same for the steel industry and so on.

"Third, I would institute a program to rebuild the infrastructure . . . especially of our cities . . . transportation, water, waste treatment. . . . I would use it as a major employment stimulus."

"Fourth, I would send to the Congress the American Defense Education Act. . . . It would dramatically increase federal aid for education, under a rationale that this is crucial to a strong America.

"Fifth, I would look into the military ranks and find those who understand 'military reform.' If I found a colonel who understood about military reform, I'd make him a general. And if I found a general who understood, I'd probably make him chief of his service."

His audience did not understand what he meant by the shorthand label, military reform. So he gave them this explanation:

"We ought to talk first about people. People fight best who fight with people they know. . . . There is entirely too much rotation of troops."

He talked about Vietnam, strategically: "The strategy of attrition was a primitive concept. It is likely that the next enemy can outman and outequip us." He favors, instead, "maneuver warfare -- outthinking your opponent."

He talked about hardware, moderately: he opposes the MX missile, favors the Cruise missile, opposes the B1 bomber, favors the Trident submarine.

He talked about the Navy, sarcastically: "We have structured our Navy beautifully -- to fight the Imperial Japanese Navy.

And he talked about the Middle East, confidentially: "There are statements made by senators, not on the floor of the Senate, but in the cloakroom; I do not think senators who supported Israel are moving away from Israel, but they are moving away from the Begin government."

That got him into a subject that has become a special concern of his: our next war. "If a major oil supply were cut off, I expect this president would send troops to the Persian Gulf immediately," he said. "There are all sorts of reasons why this would be a tragedy. One, we do not need to do it (because we have enough oil resources outside the mideast). Two, it is not our oil. Three, we wouldn't win if we went after it."

He paused. "I have a 16-year-old son. I don't want him to lose his life in Saudi Arabia."

For all his emphasis on the politics of newness, Hart is banking on the basics of politics to deliver him from the quasi-anonymity of his low, single-digit standing in the early polls. Asked how he thought he could win the presidential nomination, Hart responded, "The answer is pretty boring -- precinct organization."

Hart has mapped strategy with his top aides, among them William Shore, who will handle the campaign's day-to-day operations, and Kathryn Bushkin, who will be press secretary. Both have already earned reputations for being quick and insightful in promoting the political interests of their boss.

Hart lost a certain degree of expertise earlier this year with the resignation of his administrative assistant, Larry Smith, who is wise in the ways of the first primary state, New Hampshire, having worked for that state's former Sen. Thomas McIntyre. Smith says he simply decided that he did not want to run a presidential campaign after all. He left Hart to become an outside consultant, although he still has only good words to say about Hart and his presidential prospects.

It was partly good fortune, and partly good staff work, that enabled Hart to score political points in his first visit to New Hampshire and Massachusetts. He made the trip the day after Kennedy announced that he would not run for president in 1984. The timing was fortunate -- the trip had been scheduled days earlier anyway, but quick-reacting aides beefed up the schedule, and Hart wound up making a good impression on New Hampshire's politically active leaders when presidential politics was suddenly very much on their minds.

"He did very well," said state executive council member Dudley Dudley, who with the defeat of the incumbent governor is now highest- ranking Democratic state officeholder.

Dudley was cofounder of the Draft Kennedy movement in 1980 and had indicated earlier in the fall that she was looking elsewhere for a candidate who can recover the presidency for the Democrats.

"What impressed people most about Gary Hart was his thoughtfulness in answering questions," said Dudley, who remains uncommitted to a presidential candidate in 1984. "He did not just give quick, standard replies. He considered the question and then gave very intricate answers. It was refreshing."

During most of his trips this fall, Hart spent considerable time recruiting field directors he knows from his campaign manager days.

Political pros say Hart has gotten commitments from a number of the best. Perhaps his prize catch is William Romjue, who organized Iowa for Jimmy Carter in 1980 and has agreed to do the same for Hart.

Iowa is presently the only state in which Hart has a full-time operation underway. It is a state where presidential candidates sell themselves like Tupperware, door-to-door. Organization counts heavily there.

And, like nearly every other presidential candidate, Hart figures he needs a good showing in this first contest of 1984 to demonstrate to the rest of America what the polls and endorsement lists so far have not -- that he has enough support to rank with the major contenders, that he can win.

Still, issues are what matter most to Hart.

Ask how he contributed most to the Democratic candidates this fall and he beams most proudly when he heard a successful congressional candidate in Illinois, Dick Durbin, tell reporters he borrowed freely from Hart's position papers because they were the most helpful materials he received during the campaign.

Asked to compare himself and his prospects with the current favorite, Mondale, and the recently-abdicated front-runner, Kennedy, Hart said: "In terms of our principles, our values, the three of us are very close. The difference is in the method. . . . All the time I've spent on military reform, economic reform, speaks for itself. I've tried to be experimental, analytic. On social issues, we all vote alike. The difference is the degree to which each of us is willing to be experimental."

Last June, Hart worked the Democratic Party midterm convention in Philadelphia in a politically experimental way by showcasing a seminar he conducted with three experts on defense spending, energy and the economy. As they plodded dutifully through their discourse, Hart was softspoken and at times esoteric. He seemed indistinguishable from the advisers, not really a leader, just another part of the panel.

And that is key to his problem. Gary Hart comes across as quintessential staff.

On the stump, he has seemed to lack not just force and speaking style, but even genuine emotional conviction for what he is saying. At times, he seems almost indifferent to his audience and the message he is giving them. The line on Hart is that he is unable to rise to the oratorical occas, Larry Smith,ion.

In a swing through the Midwest this fall, for example, he had just one major speech, at an Indiana Democratic Party dinner. Those in the audience came away thinking he was flat, unconvincing. Asked about that, he launched into a soliloquy of self- justification.

"I thought the crowd was flat," he began, quietly. "I've never been able to fathom crowd chemistry. . . . You can give the same speech, the same way, and get three totally different kinds of responses."

But the more he thought about that familiar criticism, the more it grated on him. "By 1984, everybody's white papers are going to look a lot alike," he continued, his voice rising in decibels of intensity. "There's an awful lot of cross-fertilization -- plagiarism. But leadership in the '80s will be based on who pioneered the issues, not on who can give a good speech."

He paused, and suddenly he swept his arms outward in mocking exaggeration: "What else is there? Carr-izz-mah?"