THE RHETORIC of the annual budget debate is not always the best guide to the way spending patterns will actually change. The budget is by no means out of control. But it responds to deep political forces that frequently are not expressed in the cut-and-thrust of press conferences and congressional hearings. The budget responds quickly to changing currents of American opinion, but that's not the same thing as conventional party positions. If you look at the figures for the past 15 years, you will have some difficulty distinguishing between Republican and Democratic administrations.

The chart tracks two important categories of spending, both measured in billions of dollars corrected for inflation. The solid line is spending for defense. The broken line is federal payments for individuals. That's mainly Social Security and Medicare, but also includes all the other direct benefits--civil servants' pensions, unemployment compensation, food stamps, welfare payments and much else. These are the transfer payments or entitlements the rapid rise of which Mr. Reagan regularly deplores.

Defense spending rose to a peak in 1968, during the Vietnam War, but then was cut back severely in the Nixon years. The money was diverted to entitlements. In the early 1970s, a Republican president and a Democratic Congress collaborated in the fastest run-up of social benefits in American history. It was in the brief Ford administration that, again, a Republican president and a Democratic Congress began to get uneasy about these trends and halted them. The low point on that defense spending curve was 1976. Under the Carter administration, it began to rise significantly--while the social benefits flattened out until the recession of 1980 automatically pushed them up.

In many interesting respects, as this little chart suggests, the Carter administration was a precursor of the Reagan administration. Carter fiscal policy opposed steady increases in social spending, but when unemployment rose, Mr. Carter felt that he had to meet an obvious need. Regardless of its public statements, the numbers indicate that the Reagan administration has come to precisely the same conclusion. These expenditures have risen in a straight line for the past four years, with no break to hint at the point at which power was transferred from one party to the other. Similarly, defense spending follows a strikingly smooth curve of gradual acceleration going back across two transfers of power at the White House.

If we were to continue the chart for the next several years, with the figures that Mr. Reagan's budget proposes, it would show the defense curve continuing upward and payments to individuals going abruptly horizontal. Neither will happen to the degree that Mr. Reagan wishes, but defense is very likely to go higher, and social spending to slow down. In retrospect, the real change in American fiscal policy came not with the arrival of the Reagan administration, but in the Ford and Carter years.