FOR TENACITY and stamina, Sen. Pete Domenici's performance is remarkable. The president wouldn't make the hard choices on the budget. The Republican senators couldn't agree on a version of their own. Once again, it has been left to Sen. Domenici as chairman of the Budget Committee, and once again he has produced a budget that is both fairer and sounder than Mr. Reagan's.

It's not a mere paper exercise. By the time Congress adjourned last fall, the final budget looked more like the Domenici revision than the original Reagan proposal. This year's Domenici budget would allow defense spending to rise, but not at the excessive rate that the president wants. The revision drops the invidious idea of a pay cut for federal employees. Most important, it makes a serious effort -- as the president's budget does not -- to get the budget deficits down.

It's instructive to recall what happened last year. In February, after the president's budget appeared, Sens. Domenici and Mark Hatfield, the chairman of the Appropriations Committee, offered their own version. In March, it became the basis of the famous Rose Garden compromise in which, to avoid splitting his party over the huge deficit, the president accepted the congressional plan to pull it down. As it was enacted, with cuts in both defense and domestic spending, and a tax increase, it should have reduced the deficit for the fiscal year 1985 from Mr. Reagan's original estimate of $195 billion to about $175 billion.

The fiscal year 1985 is nearly half over. How is the struggle against the deficit going? Not very well, unfortunately. Instead of dropping to $175 billion, the deficit seems to have risen to $215 billion. In spite of some $20 billion in deficit reductions by Congress, it's now $20 billion larger than ever. How did that happen?

It was, as always, a series of mishaps and miscalculations. An error in legislation last year forced the government to spend an unbudgeted $14 billion to retire a certain category of public housing debt. The administration had also underestimated interest costs and farm subsidies, while overestimating revenue collections.

What should you make of it -- all the work in Congress to bring the deficit down a little, followed by the news that the deficit is larger than ever? First, the effort in Congress is crucial. It's still the only real hope of getting the deficits under control. Second, Congress will always have great difficulty accomplishing much as long as the administration has little interest in the subject. Sen. Domenici's budget deserves support as the best and most realistic prospect for getting the deficit on a downward path this year. But Congress will have to push much harder than it did last year if it really wants to see smaller deficits ahead.