MUNICH - Although it's often not heeded, standard military doctrine says: "Reinforce success" in battle.

Audi AG, down and out for years in the U.S., is riding high on styling success. But in the "battle" of the midsize luxury segment, Audi's foes - largely BMW AG and DaimlerChrysler AG's Mercedes-Benz, currently enjoy bigger artillery: V-8 engines.

Now, perhaps more responsive than ever before to U.S. consumers' desires, Audi is reinforcing its success on the styling battlefront with help in the engine bay: Audi engineers here show their midsize A6 sedan and station wagon (Avant), re-configured to carry V-8 power for the 2000 model year.

It's a serious phil-osophical thrust for Audi; to now, the company has ascribed to the notion that midsize cars don't need V-8 motivation. Case in point: the largest-displacement engine currently offered in the A6 worldwide is the 2.8L DOHC V-6.

Yet in the cheap-gas U.S., chief rivals BMW and DaimlerChrysler, along with domestic and Japanese interlopers, are reaping disproportionate rewards by offering

V-8-packing luxury midsizers. Audi's

6-cyl.-only strategy in this segment clearly is no longer realistic. Or remunerative.

Determined to make up for lost time (and profits), Audi engineers reached into the technology bag and pulled out their favorite trick: a 5-valve-per-cylinder head for the formerly 4-valve 3.7L and 4.2L DOHC V-8s.

For North America, however, only the 4.2L V-8 will be offered for the A6; also, there will be few other running-gear choices, as all 2000 A6 4.2s also will be fitted with quattro all-wheel drive and 5-speed Tiptronic automatic transmissions.

The A6 4.2's new V-8 develops 300 hp at 6,200 rpm and 295 lbs.-ft. (400 Nm) of torque from 3,000 to 4,000 rpm. Audi devotees will note that the A6 4.2's 300-hp rating is the same as that available from the current 4-valve version 4.2L V-8, right now offered only in the A8 flagship. Not to worry, say Audi engineers: for 2000, the A8's 4.2L V-8 will undergo the same

5-valve treatment, but the A8 4.2 will prevail at the top of the Audi pecking order by virtue of a 310-hp rating.

In the U.S., Audi's V-8 displacement of 4.2L fits directly beneath BMW's 4.4L DOHC V-8 and Mercedes-Benz's 4.3L SOHC V-8 - its 300 hp, however, bests both rival engines; the BMW develops 282 hp and the Mer-cedes 275 hp. And fitting the 5-valve heads on the V-8s for both the A6 and A8 means every engine Audi sells in the U.S. will employ 5-valve design.

The fitment of the V-8s in the A6 was anything but a "no-brainer." Obviously the engines fit, but engineers admit that "extensive modification" to the underbody, sidemembers, tunnel area and exhaust was necessitated by the larger engines.

"We didn't just drop the V-8 in the A6," says one Audi U.S. representative. "From the firewall forward, it's a new car."

This means an increase of 1.6 ins. (40 mm) in overall length, all accounted for from the A-pillar forward - along with a 1.5-in. (38 mm) increase in front track - to accommodate the V-8. Visually, the V-8 carrying A6s are distinguished by a ride height lowered by around a half-inch (10-mm) subtle but noticeable fender-flaring and a restyled grille/front end. The fuel tank is enlarged to 18 gals. (82L) over the 15.5 gal. (70L) lesser-engined A6s can lug.

Underscoring the reason for the A6 3.7 and 4.2's development, Audi says it expects the U.S. to be the largest market for the V-8 equipped A6, with an expected volume of approximately 3,000 units of the total 20,000 A6s Audi believes it will sell during the 2000 model year. Although the current U.S. mix for the A6 runs a significant 18% for the Avant, Audi says there are no plans to offer the A6 4.2 in the Avant body style; V-8 equipped A6 Avants will be sold in other markets, however.

We get the A6 4.2 this fall, complete with standards - apart from those already mentioned - like 16-in. wheels, leather and Audi's new Sideguard head-level side-impact air bags. What we don't know yet is the price, but Audi officials say they plan to launch the A6 4.2 with an aggressive price point - somewhere above the current V-6 car, obviously, but perhaps pleasantly below the pricey A8 flagship.

Oh, about the A8. If one takes a more insidious view of Audi's precedent-setting move to offer the A8's V-8 engine in the midsize A6, it could be viewed as undercutting the mighty A8 (especially the smaller-engined 3.7L car), as well as a tacit admission that A8 just isn't doing the job of snaring the big-fish customers, at least in the U.S. Here, sales of the genuinely advanced, all-aluminum A8 are inexplicably - and for Audi, bent on promoting technical innovation as a primary brand image - frustratingly weak.

The A6 4.2 drives spectacularly and the styling can't be ignored; it looks particularly mean with the newly hunkered-down ride height. The A6 4.2 seems like an overdue formula for grabbing those cash-laden customers currently swarming to BMW and Mercedes, and on whom the message of the A8 apparently is squandered.