YOU MIGHT CALL IT THE first Carter half-budget. He inherited it from the Ford administration and, since he had only a few weeks in which to work on the figures, it's interesting to see which ones he chose to change. Most of the revisions reflect his previously announced strategy to crank up the economy and pull it faster out of the recession. It's a cautious strategy, and it's still a rather tight budget for a new Democratic administration coming into office in a time of high and prolonged unemployment.

Evidently the President has decided that he'd rather aim a bit low in this first cut at a fiscal policy. If the economy's performance continues to be disappointing next summer, there will be time to expand it then. But if he were to aim too high and call for too large a stimulus now, he would have great difficulty persuading Congress to turn it down later. Mr. Carter is not so willing to trust the economic forecasts as his predecessors were.

The largest single change that he has made in the Ford budget is, of course, in public employment. The Republican administration never cared for the idea in principle. It wasn't simply the cost alone. The Ford budget argued that public service jobs could at best absorb only a small fraction of the millions of people unemployed. Most of the new jobs would have to come from private employers in any case, it reasonsed, and consequently it would be better to aim federal policy directly at expanding the private sector. There's a good deal to that argument, in normal times. But the unemployment rate has been over 7 per cent continuously for well over two years now. That has meant sharply higher obstacles for the young, the blacks, and the uneducated seeking to enter the labor market.

The country is currently spending about $2.8 billion a year for public service employment. Mr. Ford proposed to cut that appropriation in half for the year starting next October. Mr. Carter, in contrast, proposes to double it, raising the number of jobs from the present 300,000 or so to 600,000 by the end of this year and 725,000 in 1978. Even with that massive increase, there will be only one public service job for every eight or nine people looking for work. But the Congressional Budget Office recently published a brief profile of the people who were in this kind of federally funded employment and training program last year. Slightly over half belonged to racial minorities, some 60 per cent were under 22 years old, and the same proportion had not finished high school. Some of these people would face a very long wait before private industry put them on the payroll. Most of them face the chicken-and-egg puzzle of needing prior experience in order to get a job. Giving them a measure of experience is a decent and constructive use for public money. True, it's going to be hard to turn the appropriations off when the economy picks up momentum. But for the next year or two, that is going to be the last of the country's troubles.

Although they have no impact on fiscal policy, some of Mr. Carter's budget cuts are worth attention - especially in energy research. He has reduced the funds for the breeder reactor, a project that appears more and more dubious as its implications become more clear. The budge for the breeder is still going to be very substantial - more than half a billion dollars for 1978 - but not quite so lyrical at the departed Ford administration had proposed. Mr. Carter has also cut the funds for fusion research, another very long-term investment. Instead, he's going to put more money into the strategic storage of oil, an immediate insurance policy against future embargoes and other international tantrums.

Mr. Carter's revision of Mr. Ford's work has been not at all revolutionary. One gets the impression that the reason is not merely a lack of time. It's a matter of temperament. The emphasis in the budget has changed, in several important places, but not more than that. Carter believes in changes - but change by degrees.