HOW concerned should Americans be about their declining savings rate? Thrift has long been respected in the United States, at least in personal and family affairs, and that respect probably survived even the high-living '80s.But the rebound in savings expected as baby boomers progressed into middle age isn't materializing, according to a recent report in the New York Times. The implications of continued low savings are said to include drooping investment and flagging productivity. Those phenomena, however, may have only a thin connection to savings rates. A lot of other factors are at work in today's economy - like the still expanding federal deficit, now joined by state and local deficits, and general leeriness among lenders. The amount of debt in the country is well into the trillions, with government holding a rapidly growing share. Today's low savings rate is sometimes thought of as a peculiarly American failing. The Japanese, for instance, put away a lot more of their earnings. But Japanese workers can't look forward to having the equivalent of Social Security after retirement; they have to salt more money away. More Americans are homeowners than their counterparts overseas. Isn't that a form of saving, of putting money into an asset that can be drawn on for later needs? Any investment gap created by low savings has been largely filled in recent years by money from abroad. In effect, savings readily move across borders in today's world. Of course, the long-range implications of a dependency on foreign capital concern many Americans. For millions of Americans, what money they can accumulate now is going toward bills and whittling away at the debt piled up in recent years. Opinion surveys indicate a continued affection for savings, coupled with a concern that putting money aside is likely to become even more difficult in the future. It's probably not that people today think only in terms of spending (consumers are increasingly cautious, according to indexes of their confidence), but that other obligations are keeping many of them from saving. That picture can, and no doubt will, change.