Gov. Douglas Wilder was expected to do well in Maryland's early-bird presidential primary. A recent poll showed him leading all Democrats, with strong support coming from blacks in Prince George's County near the governor's home state of Virginia. With Wilder out, Arkansas Gov. Bill Clinton, who came in second in that poll, is the front runner. He has more money, a better organization and, in Maryland and elsewhere, strong support from elected Democratic officials. Eighteen Maryland state senators and 36 delegates have already endorsed him. With Wilder on the sidelines, Clinton, the only Democratic presidential candidate with a history of winning large-scale black support, has suddenly become formidable in what may be the most influential Maryland primary in years.