General Motors Corp. officials said yesterday that they will reject a new government petition for the recall of the company's 1980-model X cars.

"It's just smoke," a GM official said of the government's weekend request that the company recall 1.1 million 1980 X-models because of possibly defective power-assisted brakes.

The National Highway Traffic Safety Administration says it has received 509 complaints, involving 106 accidents and 31 injuries, related to the alleged defect.

The alleged defect involves power brakes that require excessive pedal pressure to stop the car.

GM is in federal court here facing charges that it knowingly put 1980 X cars on the market with rear brakes that could lock up and cause drivers to lose control during moderate to hard stops.

The NHTSA, through the Department of Justice, is asking for the "immediate" recall of 1980 X cars and is seeking a $4 million fine against GM in that case, which began March 13. Court sources speculate that a decision may not be reached until December 1985.

The new request for a recall is separate from the court case.

Some GM sources speculated yesterday that the government is trying for a public relations comeback, largely because GM made headlines last week with arguments that federal and state data show that the 1980 X cars are as safe as comparable 1980 models produced by other manufacturers.

NHTSA spokesman Richard Burdette yesterday told the Associated Press that the latest recall request "represents a judgment by investigating engineers that we will be able to prove at some point in the future that a [brake] defect exists. It asks for a recall so that we don't have to go through the long procedure" required to force one.