New York--Yahoo! Inc. CEO Timothy Koogle resigned Wednesday amid warnings from the company that its first-quarter sales would be far worse than originally expected, due to the sagging online advertising market. The Internet portal, which serves 185 million users, said it expects sales of $170 million to $180 million for the quarter, its lowest level since the end of 1999. At the end of 2000, analysts had expected Yahoo! to report $320 million in first-quarter sales. Then, in January, Yahoo! lowered its sales expectations to $220 million from $240 million. Sales for Yahoo! have been hammered because advertising from Internet companies has taken a precipitous fall and in the slowing economy national advertisers have been slow to replace them.