The success of Audi's relentless shoving for a permanent and respected place among Germany's auto giants can no longer be denied. Nor should the drastically conceived, beautifully redesigned Audi A6 4.2 be considered anything but a perfect contender to, even a potential conqueror of, the mid-size magic made for so long by Mercedes.

OK, so there's still nothing in Audi's attic that will rock, rattle or rival Porsche's high performers. BMWs will continue to be a fixation among enthusiasts interested in quick and nimble and better-handling sport sedans. Nobody has a challenge for Mercedes-Benz's S-Class, a computerized house of electronics and guidance systems that with minor modifications might be capable of orbiting the Earth.

Audi--unlike Mercedes, and with BMW and Porsche ready to whelp a luxury off-roader--doesn't even build a sport-utility vehicle. In view of that overpopulation, let us light candles and thank St. Patrick, the patron saint of safe travel across soggy farmlands and peat bogs, for such a high blessing.

But Audi does have its spunky TT coupe and roadster as novelty purchases among an impressive range of more practical cars stretching from dinky to luxurious, with a very capable Avant wagon in between. The wizards of Ingolstadt offer S (for sport) models for searchers of enhanced performance; also repair and maintenance warranties that are virtually endless.

High-value packaging is a given of Audi's basic buy, as is judicious use of Quattro all-wheel drive and turbocharging for vehicle safety and owner satisfaction.

Therein the zeitgeist of Audi.

And adding to that sturdy brand image, the $49,000 A6 4.2, the first model in the 3-year-old line to be born with a V-8, which makes the car a 300-horsepower alternative to Mercedes-Benz's all-conquering E430--which costs a little bit more and works with a lesser set of muscles.

If you want to add the Lexus GS 400, BMW's 540i and Jaguar's new 4.0 S-Type to the list of competitors, all within the A6's price, power and panache range, Audi will not be offended. Nor should it be worried.

The 4.2 is the pick of a litter of four variants of A6. Shapes range from sedan to wagon. Engine choices are last year's 2.8-liter, 200-horsepower V-6; a new 250-horsepower V-6 with twin turbochargers; and the mighty, truly powerful 4.2-liter V-8 transplanted from the venerable A8. Transmissions in this amalgam of Audis include a five-speed automatic, a Tiptronic and a six-speed manual. All versions will be available this month, with prices tripping from $34,000 for the A6 2.8 to $49,000 for the 4.2.

Visually and mechanically, by the quality and taste of its luxury appointments and the width of the performance envelope, the 4.2 is the touring car stunner that Audi has been laboring toward for years.

Owing to the size of the engine, its shape is shared with no other A6 in the lineup. The car is wider and flatter, with lower side skirts and oversized fender flares ove r optional 17-inch wheels. Such clear borrowings from Audi's touring car racing program deliver a bulldog-squat front and rear that are suggestive of some very serious horseplay. Out of my way. Fear this.

Yet what is menacing from head-on and directly behind softens as viewing angles change until a bold warning is transformed into a gentle invitation to elegant travel. Bib overalls from this side, a tuxedo from the other. Think Tom Selleck.

The interior is Bond Street meets the Louvre. Woods are sycamore and walnut, and even the sew pattern of the upholstery is made part of the design. So are textures of the various leathers and fabrics, and the depth of burnish on the aluminum trim around vents, gearshift and door handles.

All of which feeds into an Audi innovation--the creation of custom environments for the car, for your emotional ease at the wheel.

Two such atmospheres exist for the 4.2. Ambition is rich, dark walnut trim with bottle-green and storm-gr ay leathers; the aura of a classic touring sedan. Ambiante evokes a Mediterranean ambience with lighter woods and bolder colors; the effect is Tuscany at noon. Double olives on your pizza?

Beyond looks, however, the 4.2 is a triumph of space, small but wonderful conveniences and perfect ergonomics. Eight hundred miles in a day--and we did it twice--is no crippler because seats bolster torso and waist, and 12-way power positioning is infinite.

There are puddle lights in the door to make sure one doesn't step into--well, puddles. Fiber optics are used to illuminate switch symbols and door handles, and ceiling-mounted diode lights add a dim, gentle maroon illumination to the instrument panel. With the car parked downtown, remote controls seem strong enough to work from the 'burbs. The flat-bottomed trunk is deep and big enough to double as a 300-bottle wine cellar--although continual 800-mile trips would probably turn your grand cru Burgundies to mouthwash--and the 140-watt eight-speaker sound system is virtual home theater.

Standard features on the A6 4.2 are far from standard. Such as side head air bags, Quattro all-wheel drive, dual-zone climate control, front and rear reading lights, a Tiptronic manual transmission alongside a five-speed automatic, forged alloy wheels, cruise control, plus all those museum woods and Bellagio leathers.

The multi-link and double-wishbone suspension--plus heavy use of aluminum in the chassis, body panels, side-impact beams, door frames and mechanical componentry--provides a lighter but stiffer platform, adding new security and balance to more aggressive handling.

And that five-valve 4.2-liter V-8, with variable camshaft control and a three-stage, variable-length intake system, triumphs where early A6's failed in the power department and simply begs one to sin.

In early ranges, in quieter moods during ordinary moments, the A6 ambles along humming to itself. When juices stir and there are miles of broad highways and mountain wrigglies to get behind thee, the engine's harrumph becomes a big animal growl as the power comes on. And on, and on. Until 60 mph from rest shows up in 6.5 seconds. In Europe, 130-mph cruising is a walk in the Ardennes with 150-mph-plus as the run-out speed.

Yet it's all smooth, very serious, even underestimated speed with tons of grip and huge margins of steering and braking to forgive those prone to high-performance blustering beyond their skills.

It's pretty obvious that Audi's big A6 was designed to pry the E-Class jewel from Mercedes-Benz's crown. It follows that Audi's aging flagship A8 will soon undergo a major, presumably more powerful refit.

Which may mean something predatory to loom large in the rearview mirror of Mercedes-Benz's mighty S-Class.

2000 Audi A6 4.2

Cost Base, $48,900: includes eight front and side air bags, cruise control, power steering, five-speed automatic transmission with Tiptronic, all-wheel-drive Quattro, leather seats a nd wood trim, glass sunroof, Bose sound system, dual automatic climate controls, forged alloy wheels, power windows and doors with remote control, anti-lock disc brakes. As tested, $55,000: adds 17-inch wheels, high-performance tires, heated seats, solar sunroof, xenon headlights and navigation system.

Engine 4.2-liter, five-valve V-8 producing 300 horsepower.

Type Front-engine, all-wheel-drive, high-performance luxury touring sedan.

Performance 0 to 60 mph, as tested: 6.5 seconds. Top speed, manufacturer's estimate, electronically governed: 154 mph. Fuel consumption: 18 miles per gallon city, 26 mpg highway.

Curb Weight 3,800 pounds. The Good: A lusty V-8 for A6, no longer short on grunt. Wider, flatter car with lowered and aggressive look unique to 4.2. Comfortable elegance in top-quality luxury interior, with all-wheel drive topping list of premium accessories as standard equipment. High performance with balanced ha ndling and German heft, more air bags than occupants to protect. Three-year, 30,000-mile warranty including free maintenance.

The Bad: A little thirsty on gas.

The Ugly: Not from any angle.