THE BUDGET negotiators for the president and Congress won't reduce the deficit substantially unless they venture where the money is. There will have to be a sizable tax increase as well as spending cuts; the spending side of the budget can't bear the burden alone. On the spending side, it is not just defense that needs to be addressed but the net cost of Social Security.

Defense is a fourth of all spending, Social Security a fifth. Together with interest on the debt they make up 60 percent of the budget. The rest -- all other programs, from Medicare and Medicaid to farm supports and highway grants -- would have to be cut by something like a third to bring the deficit to zero on its own. That neither will occur nor should it. A Social Security cut would both reduce the pressure on the rest of the budget and legitimize cuts in other major benefit programs. If the elderly are contributing to deficit reduction, then other groups can be expected to do the same. If the elderly are not, then all groups have an out.

The budget negotiators all understand these outlines of the problem. But the politics of the dispiriting exercise have so far pointed in the opposite direction from the math. No one wants to be the first to do what everyone knows has to be done. Progress has been oblique at best, and the negotiators are running out of time. Among other things, if Congress is to hit its election-year adjournment target, the appropriations process must begin soon -- if not with the guidance of a budget agreement then without it.

The politics can be balanced just as the budget can. The president can offer political cover on taxes just as the Democrats can on Social Security -- if they will. The commonest proposal for cutting the cost of Social Security is a one-year suspension of the cost-of-living increase in benefits. The advantage of that is that it would let the negotiators suspend other indexing on both the tax and spending sides of the budget. The disadvantage is that it would hurt the poor as well as beneficiaries who could afford it. A better way to reduce the cost of Social Security would be to subject a larger share of benefits to the income tax. That would provide the protection for the poor (who generally owe no income tax) that an across-the-board reduction in benefits would not.

But the dreary circling of the problem that has characterized the talks so far must end. The next two weeks are crucial. After them will come time off for the Fourth of July, then just a few weeks until Congress' planned August recess, then just a few weeks more until the planned early October adjournment date. The longer they wait, the closer will be Election Day. It isn't going to get any easier.