THE CARTER ADMINISTRATION is now beginning its second year but, oddly, a great many Americans still say they have no clear view of it. For them, Mr. Carter and his central purposes have not yet come into focus. Along with all the other evidence of it, there was the poll that this newspaper published Sunday suggesting that perhaps a third of the voters who were questioned neither strongly approved nor disapproved of the Carter presidency. They put themselves somewhere in between. It wasn't ignorance or unconcern. It seems to have been a sense that the record so far is enigmatic.

Public ambivalence toward Mr. Carter, you could argue, is rooted in public ambivalence toward federal power and the use of it. There's a lot of dissatisfaction throughout the country about the way in which the economy is moving, for example, but there's no durable, muscular majority for any single line of action. The worries about unemployment just about balance the worries about inflation. The pressures for higher business investment counter the pressures for bigger budget deficits.

You can see this kind of division in two of the major organizations devoted to economic progress for black Americans. In addressing energy policy, the NAACP is following the strategy of growth, on grounds that the condition of blacks will improve only amidst improvement for the whole population. The Urban League puts its faith in allocated benefits and direct federal intervention in behalf of those who need it most. Both positions are intellectually respectable. But they point in opposite directions, which is hard on a politician trying to respond to the concerns of blacks.

Mr. Carter has contributed to the confusion by the shifts in his own positions. His views on the federal role seem to have gone through three discernible stages. Two years ago, when he was campaigning for the nomination, he was a small-government man. He had accurately sensed that a lot of Democrats were fed up with the steadily increasing reach of federal regulation - a trend that, we might observe, had continued rapidly through the eight years of Republican administration. Mr. Carter spoke to that resentment, which is a very large part of the reason he won the nomination. The other candidates were all much closer to the party's tradition of expansive and confident intervention.

But once Mr. Carter became the nominee, he wanted and needed the support of all the other Democrats - the one that judged a man's sincerity by his willingness to push the big bills and the big programs. Through the campaign, and the euphoria of the first months in office, Mr. Carter committed himself to that long, cumbersome succession of comprehensive reforms - of welfare, of energy policy, of taxation, of governmental organization and all the rest. None of them seems to be doing very well at the moment. Mr. Carter, who is not slow to see these things, now appears to have shifted emphasis once again within the last several months. Currently he is back to talking about the need to keep the federal government within its proper bounds.

Perhaps it is true that the political base does not exist in this country today for forceful reform legislation and large new initiatives. The American mood today is not the ebullient self-satisfaction of, say, the middle 1920s. There is an uneasy sense of obligations still to met. But there is littlew consensus on an agenda, or any widespread impulse to pursue it. That was true two years ago. The polls suggest that two years of debate, and one year of President Carter, have not done much to change that fundamental condition of our national politics.