Prickly U.S.-French relations show no sign of ebbing now that France has a new President. White House aides were miffed when Jacques Chirac upstaged President Clinton at the economic summit in Halifax by rallying leaders behind an expanded U. N. peacekeeping force in Bosnia. Chirac's tte-a-ttes with Clinton went over like a flat souffle. "He has strong opinions," sniffs one top Clintonite. "But there isn't always the knowledge or thought underlying them."