THERE IS SOMETHING vaguely Mosaic about the delivery of these Carter administration policies: energy, welfare, economic and (now) urban. Tablets are what we get, produced at long last and borne down the mountainside by the leader, who has been consulting in the misty reaches of some other realm . . . while the waiting multitude wondered what was going on. Mr. Carter likes to get ideas and intentions and imperatives put in writing. He likes to gather the relevant policies in one place. He likes to see the thing whole ("comprehensive") -- or to try to, anyway; government policy resists this kind of rational codification, and no subject resists it more resolutely than city-connected affairs. In fact, the huge and messy aggregation of governmental actions, programs and policies Mr. Carter sought to address yesterday may be said to constitute its own very special form of urban sprawl.

The point is this: Just about everything a president and his administration do has an impact on city life, and, willy-nilly, they are making "urban policy" everyday. So there is something self-evidently artificial about the elaborate, if not elephantine, attempt at drafting and promulgating such a comprehensive policy in a several thousand well-chosen words. One of the most important urban-policy decisions the administration made in the past year, for instance, was to seek a major tax cut, thereby drastically reducing the amount of new money that might be available for federal urban-spending programs. And probably it is safe to say that turning the inflation around, if the admisistration could conceivably do that, would have more to do with saving distressed cities than any of the special aid projects envisioned in Mr. Carter's policy statement.

We say all this not by way of dismissing the president's effort, but rather by way of calling attention to what may be its most valuable part: the painstaking governmentwide review of all the programs anyone could think of that may have an effect on the nation's cities and the subsequent dicision to change many of those programs that have been working to the detriment of urban social and economic health. For the administration accumulated an abundance of new evidence that in a hapahazard, unplanned way the federal government has been financing the movement of people and jobs away from the cities in much of its tax, housing and transportation policy. And it strikes us as reasonable that Mr. Carter intends not only to gain control of these and other scattered "policies," but also to insist in the future on some kind of urban-impact analysis on the part of federal agencies dealing in programs that, though seeming to be unrelated, actually have a profound effect on some aspect of urban life.

Never mind for now the rococo programs details. The two overarching themes of the president's policy are economic development and jobs. By means of various federal incentives and direct-aid programs, he hopes to reverse present trends of deterioration and to help restore some appreciable measure of evonomic vitality to out worst-off communities. If is a truism that the president is not seeking to put a lot of new money into the effort, primarily for the very good reason that there isn't much available. What his plan aims to provide could best be described as a collection of tools that -- if imaginatively used by state and local governments and private businesses and civic groups -- could make a difference.

To the extent that Mr. Carter's policy actually gets down to the crucial and inflammatory business of divvying up scarce money and resourcees, the president has made good choices and, perhaps, politically tough ones. While the administration makes much of the fact that no special region or group is being favored in this plan and that rural communities will benefit from some of its provisions, Mr. Carter has called for a channeling of funds and other assistance to especially hard-pressed people and places -- "targeting," as it is known in the trade. He could have yielded to the politically safer impulse to spread the goodies excessively thin but everywhere, but he took the more responsible course.

At least on paper -- and prospectively. That is the important thing to remember about the couple of pounds or so of program and policy that have been worked up by HUD SEcretary Patricia Harris, the White House's Stuart Eizenstat and the rest and accepted by the president. The administration now has a written urban policy. Hard, as that may have been to accomplish, it may turn out to have been a breeze compared with putting the policy into effect.