President Clinton today nominated Pamela Harriman, an accomplished political operator with long-established networks of rich and powerful friends on both sides of the Atlantic, to be Ambassador to France. Mrs. Harriman, the 73-year-old widow of Gov. Averell Harriman of New York, is the doyenne of Democratic politics and a leading fund-raiser and donor. It was to Mrs. Harriman's elegant Georgetown house, with its Van Goghs and Picassos, that the Clintons journeyed for their first gala dinner aft...