CONSULTING public opinion is always a treacherous business and that is not only because the public is fickle or the sampling is suspect. What people tell you they think when you ask about "the appropriate role of national government" or "whether the budget is too big" is often inconsistent with their reactions to specific cases that fall within the purview of those large concepts.

Last month, for example, the Gallup poll asked people what they thought about the Reagan programs. The poll confirmed the administration's view that a majority (55 percent) approved of the president's plans to cut the federal budget. What areas would they like to cut? Here's the interesting part. No area of federal spending was selected by more than 42 percent of respondents, and only three areas--welfare, food stamps and farm subsidies--were chosen for cuts by more than one out of five people. The most popular programs? Job training--only 12 percent want more cuts here and 59 percent want increases--and environmental protection. People like the idea of budget cutting, they just don't like what it means in practical terms.

What about the perennial losers in public opinion --welfare and food stamps? They are tiny items in the federal budget but a substantial minority of Americans thinks they are too big. Last year a series of polls done for the Advisory Commission on Intergovernmental Relations revealed a curious thing. When asked about "welfare," 39 percent of those questioned said that federal aid for such programs should be stopped. But when the term "aid to the needy" was used, only 17 percent favored the cut.

"Welfare," it seems, is something that goes primarily to a bunch of big-spenders who laugh up their sleeves at the rest of us. Never mind that welfare benefits are so low in most states that they're hardly worth the effort to collect; in the public mind, welfare apparently has little to do with the "needy."

Those concerned about the very many children and mothers who do, in fact, depend on welfare might consider a quick name change--how about "income enhancement programs"? Sensible efforts to improve welfare administration would also help to weed out the abusers who--in great disproportion to their actual numbers--contribute to the program's ill-repute. But welfare programs, no matter how packaged, are likely never to have much appeal on Main Street. That is why it is so important for the national government--as the repository for those aspirations and responsibilities that have little daily appeal--to remain in charge of the protection of those who are socially and economically most defenseless.