Carter and Reagan -- does it really make a difference? The perennial question has cropped up again in 1980.

As one who actively participated in the intra-party challenge of Sen. Kennedy, I had to decide what to do when he didn't win the nomination. Without hesitation, I am supporting President Carter. I retain my reservations about his record and my philosophical differences with his approach to some matters. But I am equally clear in my new view that there is a world of difference between him and Gov. Reagan, and he is the only candidate other than Reagan who can win.

Perhaps the most obvious point in comparing Carter and Reagan relates to the Supreme Court. It is virtually certain that there will be some appointments to be made in the next four years. The Nixon appointments, in particular the chief justice and Justice Rehniquist, have already altered the balance on the court. Reagan, on his record, to say nothing of the Republican platform on which he runs, will clearly seek -- and find -- doctrinaire conservatives to put on the court, people with sufficient qualifications to survive Senate scrutiny but with a clear commitment to move the court to the right. Carter, on the other hand, has a different record: one of appointing people who not only are qualified, but are from a wide variety of backgrounds and are therefore bringing new, useful and refreshing perspectives to the federal judiciary. This, in fact, is one of the truly outstanding achievements of his presidency, and I am confident that he would bring the same acumen to bear on appointments to the court.

This is not the only matter. It is an oversimplification to paint Reagan as a monster, but a Reagan presidency will seriously alter the center of gravity of political debate and action across the board, in ways the people who call themselves "liberals" should find extremely disturbing.

Reagans, "pitch," after all, is the new laissezfaire, getting government off our backs. That sounds appealing as a general matter, but the specifics are far from appealing. For example, is government "on our backs" when it requires the cleasing of the air and water, or the safe disposal of hazardous waste? The Clean Air Act is up for renewal next year. In the name of ending over-regulation and encourageing private initiative, Reagan will declare his support for clean air and then seek relaxation of standards on the burning of coal and auto emissions and other items.

The Carter record has maintained the basic current equation between the competing interests. His Environmental Protection Agency has developed quite a sophisticated understanding of the economic costs of squeezing out the last 5 percent of regulatory protection. With Reagan, we will have a major flight just to hold on to what we have, with success being defined as having to live with some partial loss as the price of staving off a greater defeat.

Is occupational safety important? Reagan will say yes, but we need to exempt businesses of under a certain size and change the burden of proof for establishing new regulations in order to keep the bureaucrats in line. The reality is that Carter inherited it administratively to the point where business complains far less about it than it uses to.

Reagan's economics are pie in the sky: we can cut taxes, balance the budget and preserve essential government services. Carter's economics are surely not one of his demonstrable successes, but his new economic initiative at least tries to target corporate tax changes in ways that have a chance of producing vitally needed new capital formation and couples that with at least a modicum of tripartite sectoral planning. It's not perfect, but it's in the real world.

And if Reagan's economics are in the wild blue yonder, you'll believe his energy policy can succeed if you believe in the tooth fairy. Yet it is entirely consistent with his new laissez-faire for him to seriously advocate turning the whole matter over to the oil companies. Carter has made his misteps, but he is on a track that properly emphasizes conservation and alternative energy sources.

How about the poor? Reagan isn't a racist, but the poor are still disproportionately black and Hispanic, and black and Hispanic people are still disproportionately poor. The Republicans are already pushing to convert welfare into a block grant and give the money to the states without any standards or matching requirements. That wouldn't be good for the poor anywhere. The Republicans are already saying the food stamp program is too expensive, which means they think it either helps too many people or gives too much to everybody it helps, or both. Pursuing that line, as Reagan will, you can only hurt the poor as well.

Reagan says he will help the cities by creating tax subsidies for enterprises that locate in zones near the inner city. But would the subsidies he denied to capital-intensive firms that hire very few people? Would there be requirements that an appropriate percentage of those hired must be unemployed or from the areas of labor surplus in the city? And does such an idea, assuming Reagan is serious about it, constitute an urban policy when the infrastructure of our older cities -- the streets, the sewers, the water mains and the bridges -- is gradually collapsing? It may be true that the bottles are beginning to look a little more alike (Carter's Urban Development Action Grant Program is a nice example of limited public money leveraging much larger private investment), but the actual contents need to be examined very carefully.

If we struggle now over 3 percent and 5 percent real increases in the defense budget, the debate in a Reagan administration will clearly be over larger increases (as well as over direction). Settling for 5 percent may come to be regarded as a win for those who oppose an accelerated arms race.

While I have stressed domestic policy, there is obviously a list of foreign policy issues. Beyond broadsides like the question of whose finger should be on the button, it is worth asking, for example, whether the peaceful transition to black majority rule in Zambabwe would have happened under Reagan and what the future of normalization of relations with China would be with Reagan.

Nor will Reagan arrive on the scene in somnolent solitude to behave as a latter-day Eisenhower and give us a benignly passive presidency, as some suggest. Unlike 1953 and 1969, the Republicans now have a government in exile who genuinely believe in Reagan's new laissiz-faire and are ready to go to work at the process of dismantlement.

The shift in the center of gravity will occur in area after area. Rear-guard actions will be fought one after another, and often simultaneously. As for those who think it would be a chance for the Democratic Party to regroup philosophically, it must be said there will be little time to think big thoughts, and four years of lost ground will have to be regained in 1984 before we will even be in a position to move ahead.