THESE ARE hard times for the nation's cities. Federal aid is down, borrowing costs are high, local revenues are falling, and the poor and unemployed are seeking help in record numbers. These pressures are forcing cities to learn new ways to cut costs, a result that should please taxpayers but that also means fewer jobs for the unemployed.

The Joint Economic Committee recently reported that two out of five cities ran deficits in 1981. Three out of five faced fiscal trouble in 1982 -- the poor state of the economy cut revenue growth at the same time that unemployment placed new demands on service programs. In this city and in others, people are now lining up for food, clothing and shelter in numbers unseen since the Depression.

Cities are responding by raising taxes and cutting back services. Plans for capital spending have been sharply reduced. That means more of that crumbling infrastructure in the familiar form of bigger potholes, closed bridges and clogged sewers. Some cities, however, are exercising their ingenuity, stretching their tax dollars by such methods as turning services over to the private sector, recycling resources, replacing paid workers by volunteers and enlisting business help in funding service programs.

Not even the White House expects these efforts to come close to filling the gap left by reduced federal aid, but there are other benefits. Citizens feel better about paying taxes if the money is spent efficiently. This is especially true if taxpayers have become personally involved in local government.

These savings, however, come at a considerable price. The steady expansion of state and local government employment over the past decade not only meant a higher level of public services; it also provided jobs to many of the millions of new workers who entered the labor market. The federal government paid for many of these jobs directly through the several hundred thousand CETA jobs and indirectly through grants for services.

Now those jobs are being cut, and the people who held them are ending up on welfare and unemployment rolls. The expected economic recovery should eventually open up opportunities for some of them. However, even when the economy was relatively healthy, the private sector could not find work for everyone. If the pace of automation quickens, private jobs -- especially those not requiring technical skills -- may be still scarcer. That leaves open the question of whether it is better to consign people to the welfare and unemployment rolls or to keep them employed in providing useful public services.