Federal auto safety czar Joan Claybrook gave the nation's consumers her going away present yesterday -- "The Car Book," the most comprehensive guide to car-buying the government has ever produced.

The free 68-page publication for the first time pulls together everything millions of dollars of federal research has discovered about automobiles.

Crash test results, fuel economy ratings, maintenance and insurance costs, accident fatality rates, safety defects and recalls for foreign and domestic cars are listed in the publication by the National Highway Traffic Safety Administration, which Claybrook heads.

A free copy of the publication can be obtained by writing "Car Book," Pueblo, Colo. 81009.

A consumer considering buying a Chevrolet Chevette, for example, would learn from "The Car Book" that the Chevette was one of only six cars that passed the NHTSA crash test and would protect occupants in a 35-mile-an-hour crash, but its windshield popped out during the collision.

The Chevette's seatbelts, however, don't fit very well and are inconvenient to use, by federal standards.

The Chevette got 26 miles per gallon in the government gas mileage tests. Therefore, "The Car Book" calculates, using $1.35-a-gallon gasoline, the consumer would spend $519 to drive 10,000 miles. Maintaining the Chevette "by the book" would cost $366 for 45,000 miles, compared to an average of $306 for all subcompacts.

The chapter on insurance shows Chevette insurance losses average $102 a year for two-door models and $86 for four-door models, but owners of the car can get discounts from usual insurance rates. Chevrolet has issued only one recall for Chevettes, calling the 1977 models back for a fuel system problem. The same kind of information is included for every foreign and domestic car tested by NHTSA and other government departments.

The traffic safety agency has published most of the data earlier, but it was released piecemeal. By pulling it together, Claybrook said, "we hope to increase consumer awareness of the safest and best performing cars. By this means, consumers in the marketplace can directly encourage industry to improve its products to meet consumer needs.

"While 'The Car Book' does not tell people which car to buy, it tells them enough to help them make a good decision on their own," she added.

Claybrook's position on consumer matters has been widely criticized by the industry and she has been targeted for removal by some Reagan advisers.

The book forecasts a new direction in government consumer protection efforts and should be good for the auto business, Michael Pertschuk, chairman of the Federal Trade Commission, said in a speech yesterday to the International Automotive Ratings Symposium.

Pertschuk predicted that government agencies will turn from direct regulation of business to using information, "as we attempt to respond to the simultaneous desires by the American people to defend themselves against abuses, while being more wary of the heavy hand of direct government controls." a

He said publication of the government auto ratings should quickly get the message to consumers that the quality and economy of American cars has improved dramatically.

Included in "The Car Book" are results of recent NHTSA crash tests for eight new models that have come out since the agency released its collision tests earlier this year. The 1980 Ford Thunderbird, Cadillac Seville and Dodge Mirada passed the test, which is designed to determine whether an occupant would survive a 35-mile-per-hour crash.

The Renault LeCar, Peugeot 504D, Mercedes Benz 240D, Oldsmobile Cutlass and Chrysler LeBaron flunked the test. All five failed because their seatbelts were so loose they allowed occupants to hit the dashboard or windshield; the Renault's steering column also was shoved into the passenger compartment, and NHTSA said the Peugeot's structural design was "inadequate."