THE 1991 Mercedes-Benz 350SD Turbo is everything demanded by auto-safety advocates and environmentalists. But only bankers can afford it.

It's enough to make you wonder if this is the state of automotive perfection -- excellently engineered cars that few of us will ever drive.

And it's not so much that the 350SD is a "luxury car," either. You could remove its interior wood paneling and leather seats, as well as its fairly ordinary sound system, and still be looking at a price above $45,000.

We're not talking the cost of frills here, folks. We're talking hard bucks for all of the things Ralph Nader Inc. say a car should be -- things engineered to a durability and reliability that could put the most inventive product-liability lawyer out of business.

You want safety? The 350SD comes with automatically tensioning seat belts, driver's-side and passenger's-side front air bags, generous "crush zones" to absorb crash energy before it reaches the car's occupants, and side-impact barrier and roof-crush protection systems superior to any on the market. Anyone getting killed in the 350SD is either unbelted in the rear seats, or is the victim of a not-survivable-under-any-circumstances traffic accident.

Of course, all of that protection means weight, nearly 4,000 pounds of automobile in this case. But the 350SD still gets good fuel economy -- 25 miles per gallon. And though the thing runs on diesel fuel, it runs smoothly, quietly, and burns more cleanly than comparable gasoline-powered cars.

It would be wonderful if every licensed driver in America could have a 350SD, or something like it. Who knows? Maybe those people who are always bugging auto makers to build "responsible cars" could pressure Congress to give the rest of us the tax breaks we'll need to buy them.

Background: Mercedes-Benz last offered diesels in the United States in 1987, when unrealistically low gasoline prices and a bevy of unfortunate General Motors diesel cars gave diesels a bad name. Now, just in time for what could be our latest energy crisis, Mercedes-Benz is offering three diesels, all with turbocharged engines and all above $40,000. The "cheapest," at $41,000, is the 300D 2.5 Turbo. The others include the tested 350SD and the top-line 350SDL.

Complaints: Poverty. I would add a verb to describe what I really feel about that economic state, but this column appears in family newspapers.

Praise: Superb all-around engineering and craftsmanship. The rear-drive 350SD seats five passengers in perfect comfort and safety.

Head-turning quotient: It's a big, rich Mercedes-Benz. Envious folks might not love you, but none of 'em will disrespect you, either.

Sound system: How is it that a country that gave us Bach and Handel now gives us an auto sound system as mediocre as Becker? For the umpteenth time, Mercedes-Benz, please find an audio supplier who understands the joy of music in motion.

Ride, acceleration and handling: Superior marks all around. The car is powered by a turbocharged, 3.5-liter, straight-six-cylinder engine rated 134 horesepower at 4,000 rpm.

Mileage: About 25 mpg (23.8-gallon tank, estimated 590-mile range on usable volume of diesel).

Price: Base price of the 350SD is $53,900, which includes just about everything on the car. Dealer's invoice price is $43,120. Price as tested is $54,250 including $350 in transportation charges.

Purse-strings note: The price of the 350SD and other "luxury cars" soon will be affected by a 10-percent tax on the price above $30,000. Hmph. To think that we actually elect people to do dumb things like this.

Warren Brown covers the automotive industry for The Washington Post.