PRESIDENT REAGAN takes it all back. His sharp words about the detractors of his budget, according to the official explanation, were intended to include only Democrats, not the Republicans. As the authorized quotation puts it, "I wasn't talking about us." In his Los Angeles speech, he hastily struck the last six words from an acerbic sentence about "the ad hoc alternatives to our economic program from both sides of the aisle."

That's a nice try, but not very persuasive. The interesting thing about this administration, at the present stage, is that its only effective opposition is centered in the Republican majority in the Senate. It started last summer when Sen. Mark Hatfield, the chairman of the Appropriations Committee, served notice that the projections for defense spending were too high. A month later, Sen. Pete Domenici, the chairman of the Budget Committee, began circulating realistic estimates of the coming deficits with the suggestion that they also were too high. More recently, Sen. Robert J. Dole, the chairman of the Finance Committee, made it clear that in his view there will have to be a tax increase whether the president likes it or not. Sen. Bob Packwood, the chairman of the Commerce Commitee, has meanwhile conveyed the impression that he is fed up with presidential anecdotes about deadbeats buying cocktail makings with their food stamps--an impression not much mitigated by his subsequent apology for speaking too publicly on the subject.

To the extent that any Democrats at all are in the conversation over basic economic policy, they are people firmly in the right wing of their own party-- Sen. Ernest F. Hollings, for example, or Rep. James R. Jones, who is in charge of the budget apparatus in the House. From time to time some of the president's partisans make another effort to prop up Tip O'Neill as a target. But as the central villain and manipulator of the budget drama, the Speaker lacks verisimilitude. And where are the libs of yesteryear? Silent as though anesthetized.

The crucial debate on the budget is now being talked out within one small segment in the range of American opinion--the segment that is known as the respectable right. It doesn't include the single- issue crowd, or the gold zealots. But the respectable right is nonetheless right, and the debate is over the competing definitions of conservatism.

A year ago, Mr. Reagan committed himself to a lot of highly desirable goals--faster economic growth, lower inflation, a balanced budget, a tax cut and much stronger defense. Those are all good conservative purposes, about which conservative politicians and voters feel strongly. Unfortunately, out of those five goals, it is hard to find any combination of more than two that are consistent with each other. Mr. Reagan's choice seems to be to retain the tax cut and the defense program at whatever cost elsewhere. He has now formally pitched the balanced budget overboard--by way of farewell, describing the deficit as "a necessary evil in the real world." The prospect of faster economic growth seems to have receded into the misty future, and there are beginning to be dismaying hints that the commitment to lower inflation may follow it there.

That brings Mr. Reagan into severe conflict with other well-established and well-defended strains of American economic conservatism. Like any president, he is anxious to resolve the divisions in his party. But he can't do that until the conservatives have resolved their own divisions over his budget.