By design, President Carter's first full budget represents a cautious, restrained approach with a limited objective: to sustain the current level of expansion around current levels, not more and not less.

Despite a deficit of $61 billion for fiscal 1979 - only $1 billion less than the deficit for fiscal 1978 for all of the hoopla about "zero base budgeting" - budget expenditures will increase only 2 per cent in real terms.

Thus, virtually all of the $38 billion increase in budget outlays for next year - 8 per cent in money terms - represents inflation in the economy, meaning that there are only the most modest increases in social programs.

This is bound to be a sticking point with Carter's liberal constituency, which had hoped he would put forth some dramatic new programs, seeking a breakthrough to more widely distributed prosperity, especially for blacks and other minority groups.

Underscoring this disappointment is the fact that defense expenditures, which Carter once promised to cut $5 billion to $7 billion, show a boost of $10.2 billion, 9.4 per cent over fiscal 1978 - a 3 per cent increase in real terms.

Office of Management and Budget Director James T. McIntyre defended the budget as "realistic and responsive" to the nation's critical needs, and Economic Council chairman Charles L. Schultze told reporters that "the present set of policies are not crash measures to rescue an economy on the brink of recession, but to keep it going."

Nonetheless, the official figures show that compared to real growth of 5.75 per cent from the fourth quarter of 1976 to the fourth quarter of 1977, the expected fourth quarter to fourth quarter gain this year is projected at only 4.5 to 5 per cent.

Reminded that President Carter in his economic message said, "We must do better" than the record of last year, Schultz said, "Doing better means continuing to grow sufficiently to reduce the rate of unemployment. If you mean [by your question] does the President believe that having grown last year by 5.75 per cent, we should grow this year by 6.75 per cent, no the President doesn't mean that."

Inevitably, because of Carter's stress on the need to limit the federal government's role, and his emphasis on tax cutting as a main source of economic stimulus, his budget will be compared by critics to those of former President Ford.

It is true that the President made clear that he prefers the tax-reduction route to greater expenditures to soften any crisis in the economy. That point was underscored by Schultze. The CEA chairman said Saturday that if the goal of a balanced budget in fiscal 1981 is abandoned, it will be because further tax relief is determined to be necessary, and not because heavy additional expenditures had been planned.

On the other hand, congressional budget experts pointed to a subtle difference between the Carter and the Ford approach. If there are no major initiatives in Carter's $500.2 billion budget, there was no heavy wielding of the ax on expenditures either.

A special OMB analysis shows that Carter made only two small cuts in spending, compared with the "current services budget" - the one that details what would have happened to spending if no changes had been made.

One is for $700 million in Medicare and Medicaid hospital plans, a reduction designed to put a lid on escalating hospital costs. The other is $600 million trim in Social Security outlays so as to reduce excessive retroactive benefits. Miscellaneous cuts of $400 million make a total reduction from the current services levels of only $1.8 billion.

On the other hand, Carter added $9.6 billion in expenditures to the current services projections. Main itmes: $3.4 billion for energy and a fuel efficiency refund program; $1 billion for education and training (mostly youth); $1 billion for defense; and $1.7 billion for an urban program to be sent to the Hill later (this is listed as a contingency allowance in the budget).

Budget Committee experts on Capitol Hill think that there is a minimum amount of numbers juggling in Carter's budget, and that the President has a reasonable chance of sustaining an economic expansion of 4.5 to 5 percent with this budget - at least for this year.

But the plain message of the President's economic message on Friday - that additional tax cuts may be needed in 1980 and later years - is underscored by statistical material in the special analyses published with the budget.

A table showing the quarterly changes in and expenditures in the national income accounts reveals that despite the $25 billion tax cut proposed by Carter for 1979, government revenue begins to pick up sharply again early next year.

This happens because spending is charted on an 8 per cent increase path (in money terms), while the gross national product is expected to grow in the 11 per cent range. With a progressive tax system, the GNP pours in more dollars to the Treasury, taking money out of the consumer and business spending stream.

The process is accelerated in 1979 and 1980 by very large increases in the Social Security tax structure.

Another way of looking at the same picture is provided by the so-called "full" or "high" employment budget. This is an analytical concept that shows what the deficit would be if the economy were operating at full employment. (The unemployment rate at full employment, according to the budget, is currently 4.9 per cent - a level the OMB says equates to 4 per cent in 1955.)

The full employment deficit, having increased dramatically from $10 billion in fiscal 1977 to $32 billion in fiscal 1978 as a result of Carter's first stimulus package, edges up only another $5 billion to $37 billion in fiscal 1978, and then drops to $19 billion in fiscal 1980.

There are two points to be noted about this. The first, made by Schultze, is that the $5 billion increase in the full employment deficit this year is a good approximation of the limited fiscal thrust of the Carter budget.

The reason that a $25 billion tax cut doesn't provide more of a stimulus is that both inflation and higher Social Security taxes wipe out the effect of almost all of the new cuts. What little stimulus remains comes from the edging up of expenditures.

The second point is made by experts who have examined the budget carefully. The fact that the full employment budget shows a decline of $18 billion in fiscal 1980 is an indication that the economy at that point may be contracting too quickly, and may need another shot of tax-cutting medicine.

The experts are none too sure, however. Some think that Carter's economists have been extra conservative in estimating the potential growth of the gross national product, and that the economy may actually move ahead faster than projected - easing the need for greater stimulus.

The sharper-than-expected drop in the unemployment rate toward the end of last year may be an early sign of this - but needs to be confirmed by results over the next several months.

The administration's underlying short-range economic assumptions for calender 1978 call for an 11 percent increase in money GNP to $2,099 billion, which would be a 4.7 percent increase in real terms, or a fraction below last year's 4.9 percent.

The year-over-year increase in the consumer price index is estimated at 5.9 percent, down from 6.5 percent in 1978. If the voluntary anti-inflation goal is achieved, that number would be shaved anther half-point.

Unemployment for the year is expected to drop to 6.3 percent, a sizeable decline drop from 7 per cent in 1977 and 7.7 percent in 1976. For the fourth quarter, the projecton is a rate of 6.2 percent.