General Motors Corp. yesterday drew near the end of its defense of its 1980 X cars, arguing that the cars are as safe, if not safer, than comparable autos produced by other manufacturers for the same model year.

GM mostly relied on government data in making its case in the waning days of defense testimony here before U.S. District Judge Thomas P. Jackson.

The nonjury trial, which began last March 13, stems from government charges that GM marketed its 1980 X cars, even though company officials knew that those models had serious braking problems.

The suit, brought by the Justice Department on behalf of the National Highway Traffic Safety Administration, seeks $4 million in fines from GM and the "immediate" recall of the estimated 1.1 million X cars -- Buick Skylarks, Chevrolet Citations, Oldsmobile Omegas and Pontiac Phoenixes -- produced for the 1980 model year.

But GM officials yesterday reiterated their contention that no recall is needed and that the cars in question were unjustly maligned by government auto safety officials.

Using volumes of data from NHTSA's own Fatal Accident Reporting System, GM presented state-by-state figures comparing the accident experiences of 1980 X cars with those of competitive machines. The data were based on "injury vehicles per 10,000 registered-vehicle years."

A "vehicle year" is defined as each year a given vehicle is registered as in use. "Injuries" include fatalities, as well as minor and major injuries in NHTSA/FARS reporting.

The accident statistics were compiled by Roger McCarthy, president of Failure Analysis Associates of Palo Alto, Calif., the last of 11 witnesses called to testify in GM's defense. McCarthy's firm is highly regarded in auto industry and safety engineering circles for its work in vehicular accident analysis.

McCarthy's charts showed that nationwide from 1980-1983, GM's 1980 X cars were involved in 1.818 fatal accidents per 10,000 registered-vehicle years. All makes and models of 1980 cars were involved in 2.097 fatal accidents per 10,000 car-years.

Directly comparable non-GM models were involved in 2.234 accidents per 10,000 car-years, McCarthy said.

Similarly, state-by-state figures provided for nine states showed the X car compared favorably with other cars, according to McCarthy's charts. For example, according to 1980-1983 Maryland state accident reports, 360 X cars were involved in "injury accidents," compared with 4,899 for all passenger cars and 2,464 for cars that were comparable to the X cars in size, weight and general construction.

In Maryland, those figures worked out to 61.35 "injury accident" X cars per 10,000 registered-vehicle years, as opposed to 87.18 per 10,000 registered-use years for vehicles of all makes and models and 86.72 per 10,000 registered-use years for non-GM models in the X car peer group.

"In my judgment, had the government looked at this data before it filed its suit, it would not have filed the suit," James A. Durkin, GM's assistant general counsel, told reporters yesterday during a trial recess.

"This data demonstrates that the X car has a safety record that is better than or equal to any peer car on the road. If you were the government and you were about to allege that the X car creates an unreasonable risk, you presumably would have the statistics to prove it," he said.

"But the accuracy of those allegations is not reflected in the results. The data prove otherwise," Durkin asserted.

NHTSA officials declined comment, citing longstanding agency policy not to comment on court cases in progress.

But the agency is expected to present about seven rebuttal witnesses after GM completes its evidentiary testimony this week. That means the trial could last past February 1985, assuming that GM will exercise its right to rebut NHTSA's rebuttal witnesses, trial sources say.

There already are about 11,000 pages of testimony, 3,800 exhibits and charts, and reams of his own notes for Judge Jackson to consider. That load undoubtably will increase before arguments end. And that means that a decision in the case could be as far away as December 1985, some court sources say.

That expected delay, in turn, raises the question of how urgent is it to get the allegedly defective X cars fixed. Some industry estimates are that about 800,000 of the 1.1 million 1980 X cars will still be in service by December 1985.

Meanwhile, poor sales -- mostly attributable to bad publicity surrounding the X cars -- has forced GM to drop the Pontiac Phoenix and Oldsmobile Omega for the 1985-model year, according to the Detroit-based auto trade magazine, Ward's Auto World.

The magazine gave the X line its "Loser of the Year Award" and "Wrath of Washington Trophy" for 1985.