DETROIT  One of the biggest boosters of the American auto industry said Tuesday that he was bailing out of his large stake in the Ford Motor Company  a stinging no-confidence vote that raised the anxiety level in this city over the deepening troubles of the Big Three car companies.

By starting to sell off his $1 billion bet on Ford, an investment that is now worth less than $300 million, the financier Kirk Kerkorian joined the growing ranks of investors who have soured on Detroit’s prospects because of plummeting sales and mounting losses.

Mr. Kerkorian’s abrupt decision to back away from Ford comes just six months after he began building his stake. It also follows an effort by the private equity firm Cerberus Capital Management to try to sell Chrysler to General Motors after spending $7.4 billion a year ago to acquire the smallest of the Big Three automakers.

G.M. and Cerberus need banks and other investors to provide financing for the deal. But the tenuous state of the industry has made prospective investors, so far, hesitant to back the merger.