AT EACH SUCCESSIVE stage of the budget process, the federal deficit keeps coming down. This trend is now in its second year, and running strong as ever. Last January President Carter sent Congress a budget with $29 million deficit, and the two congressional budget committees have now worked out a compromise resolution pulling it down to $23 billion. The resolution goes back to both houses within the next few days, but it's not very likely to be changed. Ironically, it's mainly the current surge of inflation that's pushing the budget toward balance.

Inflation raises the income side of the federal budget faster than the outgo, and Congress is shaving down the deficit merely by adopting a more realistic inflation forecast than Mr. Carter did. But the change in congressional policy over the past two years had been remarkable. Previously, presidents and congresses spent the inflation dividends on higher outlays and reductions in tax rates. The turnaround became visible last year, after Mr. Carter offered a budget with a huge $61 billion deficit. Then came the California vote on Proposition 13. Ever since then Mr. Carter and the two houses of Congress have been engaged in a brisk competition in restraint.

These two years' budgets also depart from past practice in that neither the president nor Congress is using them to change American values or public commitments. The point was made in some detail last weekend by the Brookings Institution's annual budget review, "Setting National Priorities." You could go further and say that the last major change in the budget was in 1976, when President Ford decided that the post-Vietnam defense budget had been shaved lower than safety allowed. A concesus on the general shape of the federal budget developed that year between the Republican president and the Democratic Congress, and that same consensus continues with only minor adjustments through this latest resolution.

The House had voted earlier this spring to cut defense spending. But the president promised NATO to increase it 3 percent above the inflation rate, and the Senate backed the president. The conferees on this first budget resolution have adopted the Senate's figure. In a purely arithmetical sense, the president has been upheld. In realty, of course, the outcome is something of a compromise between Senate and House positions since-once again-the inflation rate will be higher than the administration's forecast, holding the real increase in defense spending well below that symbolic 3 percent.

The current resolution is no more than a guide. It's the second resolution, in September, that is legally binding. By that time, if inflation goes up a little, the dificit figure will come down a little more and the administration, to its own-and everyone else's-surprise, will be well on its way to the balanced budget that it promised for 1981.