Declining sales are likely to push the U.S. market share of General Motors Corp. (GM) for October to its lowest monthly level in 25 years, a leading Wall Street analyst said.

GM, Ford Motor Co. (F) and the Chrysler arm of DaimlerChrysler (DCX) have all had a dismal sales performance so far this month amid general uneasiness about the economy, high fuel prices and the so-called "pull-ahead" effect of big consumer incentive programs offered over the summer, according to Deutsche Bank analyst Rod Lache.

In a note to clients, he said GM was hurting the most, with a dealer survey indicating its October U.S. sales are down 26 percent compared with the same month last year.

If that trend holds, Lache said, GM's monthly U.S. market share would fall to 20.5 percent, its lowest level since at least 1980.

That would mark more bad news for the world's largest automaker, which posted its fourth consecutive quarterly loss on Monday and has lost more than $4.5 billion in North America so far this year.

Lache's sales figures are adjusted for one less selling day in October this year than a year ago. He sees industrywide light vehicle sales coming in at a seasonally adjusted annual rate of about 15.3 million in October, down from 16.9 million a year ago and the lowest rate since August 1998.

October sales of new cars and trucks at Ford are down 23 percent so far this month, while Chrysler's sales have dropped 13 percent, Lache said.

"We do not see the near-term sales picture for GM and Ford getting better in November," he said. He added that December sales were likely to improve somewhat.