IN THE LETTERS column today, Senate Appropriations Committee Chairman Mark O. Hatfield takes issue with our assertion in an editorial last Monday that Congress -- through the budget resolution process -- has already done much of the work of deciding next year's budget. Sen. Hatfield is right that, while the budget resolution is an important control on congressional spending, it is only the start of a long process in which detailed spending plans are developed and money appropriated for each government agency and program.

The final stage of that process is supposed to be managed by the Senate and House Appropriations committees, which will be trying during the lame-duck session to complete detailed appropriations for the many defense and non-defense programs under their jurisdiction. Thus far, only three appropriations bills for the current fiscal year have been signed into law, although several others have been enacted in the Senate or the House.

The budget resolution, passed after prolonged negotiations last June, established revenue and spending limits for each major area of government. Congress can change those limits if it wants to, but this year strong controls were added to keep the authorizing and spending committees pretty much in line.

Some budget targets have already been translated into law by means of last summer's omnibus budget reconciliation and tax bills, which raised taxes and cut back the terms of entitlement programs, such as welfare, food stamps and Medicare. Subject to the overall limit set by the budget resolution, however, the Appropriations committees retain final say on how more than $200 billion in federal money is to be spent on the so-called discretionary programs -- everything from buying weapons to running the national parks.

This year the Appropriations committees' work was complicated by the lateness of the budget resolution and the need to deal with two controversial supplemental money bills sought by the administration. But the main reason the appropriations are behind schedule is not that the budget system is faulty, but rather that political will is hard to muster when it is time to decide on the division of losses among pet programs and congressional districts. It was much easier to get appropriation bills through on time back when money flowed freely in Congress and the deficit was looked on as only the president's problem.

Now less than three weeks remain in which Congress must try to complete work on 10 appropriation measures. The committees must also develop continuing resolutions -- frequently as detailed and important in impact as final appropriation bills -- that will keep the government operating in case final appropriations aren't passed before Congress adjourns. Many acts with large consequences can get buried in these last-minute measures. That's why it's worth watching every waddle of the lame duck.