The budget: $400 billion still to go

Amid all the hearty congratulations heard in recent days about enactment of the $99 billion tax hike, it is crucial not to overlook the long distance the United States must still go in slashing unnecessary federal spending and reducing budget deficits. These are expected to total more than $400 billion between fiscal years 1982 and 1985.

President Reagan is surely aware of exactly how urgent it is that deficits be constrained if interest rates are to continue to fall - and remain down. Until that occurs, economic recovery, assuming it is hesitantly underway, is apt to prove short-lived and illusive, and the country will continue to suffer business failures, sluggish consumer spending, and a high unemployment rate.

In this connection, key White House advisers are reportedly urging the President, now on vacation, to veto a $14.1 billion supplemental appropriations bill containing $918 million in funds for college students, the elderly, and the disadvantaged which they feel are not truly needed. Veto of the measure thus becomes a tempting move for the President to show his commitment to budget cutting. It also provides a way for him to court conservatives again after his flirtation with the tax hike - considered a betrayal by Mr. Reagan's supply-side supporters.

Such a veto, however, while it would provide the appearance of budget cutting , is far from the fundamental long-range budget reform that is needed if the deficits are to be brought under control. In fact, vetoing the current measure would likely provide additional budgetary problems for the administration since, among other things, it contains funds for Mr. Reagan's Caribbean Basin initiative. The President would be well advised to sign the legislation and push forward with longer-range budget adjustments.

What can be cut? Three areas of the budget should be given special consideration:

* Entitlements, especially social security. Granted, neither the White House nor Congress will tackle the enormously costly and politically sensitive social security program until after the National Commission on Social Security issues its report later this year. Yet both the administration and key lawmakers have already proposed various reforms (such as giving retirees a smaller percentage rate of increase in benefits) that could save billions of dollars over the years. This is not a matter of cutting benefits for the neediest but of stemming the fiscally dangerous rate of growth and putting the system on a sound financial basis. Other programs, such as veterans' benefits, also need revision.

* Defense spending. Mr. Reagan has said that he will not consider major cuts in projected military spending. Yet it is because the administration went ahead with massive increases in defense outlays while granting the largest tax cut in the nation's history that it brought about the current deficit problem. According to the administration's July mid-session budget review, defense spending will total $188 billion for 1982; $222 billion for 1983; and $253 billion for 1984. Surely there is room for cutting the rate of increase in outlays without injuring the nation's security.

* Tax expenditures and subsidies. Revenue losses to the federal government (in the form of various tax exemptions and deductions for individual taxpayers) run well over $200 billion a year. Just imposing ceilings on the amount of consumer-credit interest and home-mortgage interest that could be deducted by taxpayers could bring in billions of additional tax dollars. Meantime, overgenerous subsidies to business and agriculture (to name just two powerful special- interest groups) also run into the billions of dollars. The potential for savings is great.

The challenge for President Reagan and congressional lawmakers is to turn to bold new ways of bringing the federal budget under control. Slashing pennies from already decimated programs affecting the lowest-income segments of society will not do the job and only severely call in question the President's concern for the poor. What is now needed is the political courage - and continued bipartisan cooperation - to go after the costly ''big ticket'' items. There can be few persons in authority in Washington these days who do not know what these items are.