For four years now, the Chevrolet Lumina has been the invisible family sedan, hidden in the shadows while rivals, most notably the Chrysler LH cars, Toyota Camry, Honda Accord and Ford Taurus, were updated with brand-new exteriors, more amenities and state-of-the-art safety features.

Not any longer. The latest Lumina is a great leap forward for Chevrolet, an improvement over past models by almost any measure you care to make. It is, at last, a serious contender for sales stardom in the midsize class.

The changes are more than skin deep, going well beyond the obvious and extending into the way the Lumina is packaged. The coupe version is gone. Instead, a Lumina-derived Monte Carlo revives the familiar Chevrolet model name and strives for its own identity both on the street and on NASCAR racetracks.

What's left is a pair of Lumina trim levels - base and LS, both 4-door sedans - each with its own distinct features and short list of options.

An impressive lineup of standard features is offered on both Luminas. The base-level car has, for example, air conditioning, driver and front-passenger airbags, GM's effective PASS-Key II theft deterrent system and power door locks. The LS adds anti-lock brakes (ABS) and power windows (both optional on the base model), along with fancier upholstery and trim.

But the Lumina's most compelling attribute may well be its low price/amenity ratio. The base model's sticker price undercuts some rivals by a four-figure sum. The LS beats the opposition on price, too, especially when standard equipment is factored in.

And Chevrolet has made giant strides in build quality, too. You won't find loose ends dangling or the thousand-and-one trivial faults that have plagued some past Chevrolets. Today's Lumina shows every sign of being a durable, reliable car that will outlast its warranty.

Each car in the midsize class has its own personality, strengths and features, and the Lumina can now go head-to-head in al-most every category with the best of them.