Mr. Reagan's budget speech was a sharp and effective attack on the mismanagement by that fellow in the White House, whom he never named. The question, Mr. Reagan declared, is whether the country can compel its government "to end the dangerous addiction to deficit spending and finally live within its means." Right on! The United States, he said, cannot "stay on the immoral, dead-end course of deficit spending." How true. If only Mr. Reagan had been elected in 1980, things would be different. Mr. Reagan is a tiger on deficit spending and, if he were in charge, you can be assured that there would be no huge deficit to strain and distort the economy.

We pause here for a deep sigh and a return to reality. Since the late 1960s, Republican presidents have repeatedly fallen into the habit of speaking about deficits as though they were in the opposition. The reason is simple. The spending programs are popular, and deficits produce the kind of temporary boom that is very helpful in winning elections. But good conservatives cannot approve of them, and the recent Republican presidents have usually resolved the dilemma by pretending that someone else must be doing these dreadful things. The fastest increase in social benefits in American history was not in the New Deal or the Great Society, but in the Nixon-Ford period of the early 1970s. Non-defense spending this year will be higher, both in dollars and as a proportion of GNP, than it was when Jimmy Carter left office in 1981.

Speaking of spending cuts, Mr. Reagan earnestly said: "One area we will not touch, however, is the safety net for needy Americans." Really? Mr. Reagan was advocating a cut of 2 percent a year, for the next three years, in the purchasing power of Social Security benefits. If that goes into effect, the Congressional Budget Office estimates, about 650,000 people will fall below the poverty line. There seems to be a hole in the safety net.

But Mr. Reagan is genuinely right about one thing: the current deficits are a serious threat. Those deficits are the result of the excessive 1981 tax cut. They speeded up the economy, pulling it out of the recession and producing a wave of prosperity for last year's election. But as they continue they will generate either much higher interest rates or much higher inflation. Spending cuts alone can't control those deficits. It's going to take higher taxes as well.

Mr. Reagan seems at last to sense serious trouble ahead. That's a good sign. But he is evidently not yet ready to deal with it in ways that are either fair or effective.