THE FREEZING weather that has had most people in the northern part of this country sitting by the fireplace is one of several factors pushing people away from the northern states and cities. To get warm, to get jobs, to get less expensive housing and to get away from urban decay, more and more people, according to the Census Bureau, are heading toward the Sun Belt. This movement of people and jobs away from the North further cripples communities already lame as a result of the faltering automobile, steel and other manufacturing industries. Now, the President's Commission for a National Agenda for the Eighties, a group put together two years ago by President Carter, recommends that the federal government not lend a hand to these slumping northern cities but help people get out of them. What kind of sense does that make? Good sense -- but only up to a point.

The good sense is this: no government aid program to northern businesses or communities can stem the flow of people and industry to the Sun Belt. Everything from the weather to lower taxes and fewer people -- especially fewer poor people -- is pulling people south. The history of federal aid to beleaguered cities also indicates that no government intervention on behalf of the northern cities has been very successful in stopping jobs or people from leaving. What the federal government can do, as the commission's report notes, is to help northern communities make the transition from high populations to lower populations and from manufacturing industries to white-collar service industries.

To preserve the North from economic collapse, the commission urges that the national government, with its wide tax base, take control of some nationwide programs, such as welfare and national health. That would reduce one major financial burden on the northern area governments. It would also open the possibility that those governments could reduce taxes. The commission supports "streamlining" federal grant programs by placing fewer constraints on how grants can be used by local governments. Not bad ideas. But the commission's ideas, unfortunately, do not stop there.

The commission urges that the federal government help northerners move south by offering "skill acquisition and assisted relocation programs targeted to the employable." This idea is seriously flawed. The basic principal for the federal government to follow in this situation is neutrality. The government has no business urging people to move anywhere. Where it can help and should help is in buffering people from the pain of a sudden change. But prompting people to move by giving them special job-training programs goes past those bounds.

A policy encouraging people to move south en masse may solve some current northern problems but is sure to trigger new ones, possibly more severe, for an underpopulated North and a suddenly bulging South. Problems with social welfare programs, such as public housing, will simply shift to the South. And let's not forget that the Sun Belt is not all green pastures. It too has a dependence on the federal Treasury. For instance, water is already a precious commodity in the Sun Belt. The federal government's contribution to water projects has been a necessary part of all southwestern development. Growth in the Southwest will require more water and more dollars from the federal Treasury.

The challenge to the federal government is not to promote the southward movement of people now facing hard times in the North, as the commission suggests. The challenge is to help the nation handle the change with the least damage to people in any part of the nation.