THE FEDERAL budget is now on a track leading to steadily bigger deficits. That is the first striking conclusion springing out of the Congressional Budget Office's analysis published yesterday. It offers a somber overture to the budget debate that will begin in earnest on Monday, when President Reagan presents Congress with his draft for next year. Perhaps the most useful thing that we can offer you this weekend is a sort of program for the event, before everyone dives into that bottomless barrel of numbers.

The Congressional Budget Office is still a rather new idea--Congress' counterpart to the president's Office of Management and Budget. Until eight years ago, the White House was the sole source of budget data. The president controlled it all, down to the last decimal point. Since the congressional committees worked on it separately, only the president ever had valid totals--which, as Congress knew only too well, gave him a large and continuous political advantage. People might often suspect that a president's numbers were distorted, but it could never be proved until much too late. Finally, in the 1974 budget reform, Congress set up the CBO to be its auditor, and gave it the same analytical capability that the president commanded. CBO has now published its annual reports on the state of the economy and the budget.

CBO works for two masters--the Senate, controlled by Republicans, and the House, controlled by Democrats. Its judgments are as close to neutral, in political terms, as anything that you are likely to see in this quarrelsome season. The crucial forecast for economic growth seems to be, if anything, a little high--which means that even these estimated deficits may be a bit low.

In the past, however large the deficit, this kind of projection always showed rising revenues closing the gap. Growth and inflation took care of it. But in the aftermath of last year's gigantic tax cut, that gap will get steadily wider. The administration expected this year's deficit to be down to $43 billion. Instead, the CBO says, it's now headed toward $109 billion and, if you add the off-budget spending, that's really $129 billion. That's not a forecast. It's the number that will result if the economy behaves as the CBO expects and --important qualification--if there's no change in present policy. For next year, present policy would produce a deficit of $176 billion, including the off-budget spending. And so forth into the future, steadily upward.

President Reagan intends, of course, to change current policy. But the CBO has demonstrated the magnitude of the trend. It is not credible that he can reverse it by cuts in spending alone. Either he raises taxes, the CBO warns, or he runs a high risk that the swelling deficit will send interest rates shooting up again and choking off growth.

How will Mr. Reagan address that central dilemma? The country will find out next week when the budget appears. A couple of days later he and his economic advisers will lay out the administration's position in their annual Economic Report, and Congress will begin the long job of weighing them against the CBO's calculations. The dilemma, after all, isn't Mr. Reagan's alone. It's shared by Congress and the voters. The CBO has provided an auditor's report that doesn't tell anyone what to do. But it tells everybody what's got to be done.