Likewise, the 1,100 G.M. dealers that got a letter Friday represent 18 percent of G.M.’s 5,969 outlets, but just 7 percent of last year’s sales. Nearly 500 of them sell fewer than 35 new G.M. vehicles a year, Mr. LaNeve said.

“They’re dealerships that are in most cases hurting, losing money and in danger of going out of business anyway,” he said on a conference call with reporters. “It’s a move that people could argue should have been taken years ago but this leadership team had no choice but to do it today,” he added.

The companies say that cutting dealerships will lead to higher and more profitable sales at the ones that remain, but Mr. LaNeve conceded that sales most likely would be hurt for as long as 18 months.

“In the short term there is a risk that we would lose some sales,” he said. “What is critical is that we have a healthy, viable dealer network.”

Unlike Chrysler, which on Thursday released a list of 789 dealers that it was cutting loose, G.M. did not announce publicly the dealers that it did not want.

In addition to the cuts revealed Friday, G.M. expects to shed about 500 dealers that sell only Pontiac, Saturn, Saab or Hummer, which are the brands it intends to sell or close. The rest will be achieved through attrition and by consolidating multiple franchises.

It said 90 percent of those unaffected by Friday’s cuts would be offered a chance to be part of a restructured G.M. But that could change, and the company could force dealers to shut sooner in a bankruptcy proceeding.