More dismal news from the motor industry is on the cards when carmakers report December US sales on Monday , setting the stage for a gloomy mood at next week's annual Detroit auto show, the industry's premier North American event, writes Bernard Simon .

Analysts estimate that car and light-truck sales slid to a seasonally adjusted annual rate of about 10m units last month, making December the worst month in a stomach-churning year for carmakers. Sales in December 2007 stood at 16.3m. The drop is equivalent to the annual output of about two dozen assembly plants.

General Motors and Chrysler are expected to post the biggest declines, as uncertainty about their future and limited credit available from their capital-starved financing arms kept prospective buyers away.

A $17.4bn lifeline extended by the US government to the two companies in mid-December, followed by a $6bn bailout of GMAC, GM's financing arm, have provided some breathing room.

Chris Ceraso, analyst at Credit Suisse, predicts that GMAC's improved access to funding could boost GM's sales by "several hundred thousand" vehicles in 2009.

Without a pick-up in sales, GM, Chrysler and possibly Ford Motor will be forced to seek more taxpayer support by early spring.