Ford sources say consumer buying remains strong and that the growing small-car stockpile is traceable chiefly to a drop in dealer orders, reflecting the Federal Reserve's interest-rate hikes. Because they must finance their inventories, dealers get hit immediately when rates rise and thus tend to cut back purchases from automakers when money gets more costly. But other experts suspect that buyers of lower-price models, absent major sates incentives, are also worried about higher rates -- even though up to now they've only added a few dollars to monthly payments. Still, with January sales tracking 15% behind a year earlier, the market may need a shot of adrenalin in the form of cash rebates or other enticements.