THE STANDARD FORECAST for this year's inflation - a few early months of rapidly rising prices but then a relaxation - no longer seems plausible. The April figures are especially disruptive beacuse the trend was supposed to be moving downward by this time. Prices are clearly off the expected track. Last winter's chief culprit, the price of beef, is still rising like a rocket. Now it's joined by gasoline prices and, only comparatively less spectacularly, the prices of cars and hosues. The extraordinary and damaging effects of the oil shortage are obviously contributing mightily to the pattern. But the very large price increases this spring have been sufficiently widespread that there is clearly no single, simple cause.

The classic cure is a recession, but each successive recession seems to have less effect on the inflation rate. The emerging strategy seems to be aimed, instead, at slow growth for a rather long time ahead. Restraint is now both necessary and inevitable. The country is entering a period of uneasy experimentation to see how tight the restraint can get without driving unemployment to unacceptable levels. How high would that be? It's not yet clear, but the country seems prepared to tolerate a rate perhaps around 7 percent. The mechanism for tighter restraint is going to be, simply, higher taxes.

Congress won't have to raise them. Inflation does it automatically, by pushing people into higer brackets. Traditionally, Congress has interceded regularly with tax cuts to keep the burden within accustomed limits. That tradition would normally ordain another tax cut next year. But it looks very much as though Congress is going to hold off.

That's a courageous decision and, unfortunately, it's the right one. The only really effective way to control the price of beef is to switch to chicken - if not to macaroni. The best hope for slowing gasoline prices is to stay home. Americans haven't shown much inclination to do either, voluntarily. But now the mighty engine of the federal tax system will push them into it. It's not quick, and it's not going to be a lot of fun. But nobody really has any other strategy to offer.

That dangerously candid man Alfred Kahn, the president's adviser on inflation policy, put it explicitly at the administration's somber press conference on the April figures. "There's no way we can avoid a decline in our standard of living," he said. "All we can do is adapt to it."