DETROIT  General Motors is in preliminary talks about a possible merger with Chrysler, a deal that could drastically remake the landscape of the auto industry by reducing the Big Three of Detroit automakers to the Big Two.

The talks between G.M. and Cerberus Capital Management, the private equity firm that owns Chrysler, began more than a month ago, and the negotiations are not certain to produce a deal. Two people close to the process said the chances of a merger were “50-50” as of Friday and would most likely still take weeks to work out.

A merger would be a historic event, with two of the most iconic names in American industry coming together to survive in an increasingly difficult environment. Both have roots dating back decades in Detroit and, with Ford, long dominated the auto industry  until Japanese and other foreign car makers began making inroads into the American market.

The auto industry is being pummeled from all sides  by high gas prices that have soured consumers on profitable S.U.V.’s, by a softening economy that has scared shoppers away from showrooms, and by tight credit that is making it difficult for willing buyers to obtain loans. Both G.M. and Chrysler have been struggling with product lineups that are out of sync with consumer demand for smaller, more fuel-efficient cars.