One of the most interesting public figures in America today in the field of defense policy is Sen. Gary Hart of Colorado. Like many Democratic officeholders of his generation, he is a product of the protest against the Vietnam War. He first came into public view in 1972 as the presidential campaign director for George McGovern. Two years later, at the age of 36, he was elected to the Senate in the post-Watergate landslide with important help from the remnants of the anti-war movement. If anyone seemed destined to wear deeper the well-beaten path of reflexive opposition to defense programs that many liberals follow today, it was Hart. And his first two or three years in the Senate were often in that tradition.

More recently, he has begun to confound such expectations. His distinction has been in combining efforts to force the military to innovate with -- increasingly in recent months -- support for an adequately funded defense establishment. You can find a lot of people who support one or the other of those aims, but few, especially liberal politicians, who work for both. Some of the military's political supporters are for less critical of hidebound approaches than military officers are themselves. On the other side of the political spectrum, talk is cheap about the need for military innovation. Many of those who urge it verbally are willing to play a shell game with the money it will cost -- to pretend that innovation can make possible fat defense savings immediately and negate the need for painful budget increases.

Hart has been more honest. He was recently one of only three Democrats in the Budget Committee to vote for the Hollings Amendment to increase the defense budget this -- a somewhat reduced version of which President Carter still opposed as being too generous to Defense. Hart has recognized that constant pressure for innovation is a vital part of having a successful military establishment.

At the same time, he has admitted that it costs money and takes patience and hard work. He has not merely given the military uncritical support for more resources, but neither has he taken the cheap and hypocritical shot of preaching at them to do everything immediately simpler, cheaper and better. No friend of big aircraft carriers, for example, he has been willing to build one to maintain the Navy of today's technology, but only as part of a package of programs moving the Navy toward the small carriers and Vertical/Short-Takeoff-and-Landing (V/STOL) aircraft that he prefers.

Of course, he is from a relatively conservative state and so has had a political incentive to support adequate defense budgets. But the important thing is he has done so as part of careful evolution over a period of time, protecting necessary current military programs such as readiness and shipbuilding, but at the same time promoting new technologies and tactics. He has not always succeeded, and he is not out in front on the two toughest national security issues -- U.S.-Soviet relations and military manpower -- as are, for example, two of his Democratic colleagues on the Senate Armed Services Committee, Sens. Jackson and Nunn.

But he has begun to try to establish a union of thoughful supporters and friendly critics of the military. Such complex political undertakings are hard to bring off. You can zigzag so much in order to appeal to the different constituencies that you end up, as did Clevinger in "Catch 22," of whom Yossarian said tha all his left-wing friends thought he was a fascist and all his right-wing friends thought he was a communist -- in short, he was a dope.

But Hart has avoided the Clevinger trap. Many of the most innovative millitary officers have become quite friendly with him and his staff. And his liberal supporters are occasionally a trifle sullen, but not openly rebellious. l

Hart's efforts are vitally important for both the country and the Democratic Party. Many liberals in this country were co-opted early into support for the Vietnam War, and their abiding feelings of guilt have greatly hindered their ability to look disappassionately at this country's military needs. And the United States cannot long withstand a challenge of the sort of Soviet Union is mounting today with either of its two major political parties debilitated in this way. Young, skeptical, liberal voters will listen to a political figure like Hart say things about the need for a strong defense that they will not take from one known to ba a lifelong supporter of the military.

If he proves in November that he can hold both liberal and conservative voters with his approach in a state such as Colorado, and if some of his liberal colleagues less supportive of defense are defeated, it will be a message that may finally get through -- even to those on the left wing of his party who haven't had a new substantive or political thought about military issues since they watched the Tet offensive on the evening news over a dozen years ago.