A category of cars has reappeared so suddenly that nobody has got around to christening its niche.

The European Minis started it all in the '50s. The Volkswagen GTI forged the second generation of the class two decades later. Now Honda's CRX, the Geo Storm and several gamesome, scurrying GT versions of the subcompact cars are broadening this intermittent species into a full-blown genus of the '90s.

"Well . . . yes, um . . . ah, it used to be the pocket rocket class," said John Rettie of J.D. Power & Associates, the Agoura Hills gurus who are in the very precise business of categorizing, analyzing, classifying and tabulating the vehicles we buy. "They are not sports cars.

They are not real sedans. So we lump them in with small sporty cars.

"Jokingly and internally, we call it the Flavor of the Month Division. Because they do come and go. And the new Nissan NX is going to be the new flavor."

It certainly is.

And definitely a flavor to last in the performance taste buds of those who like little cars that can.

Mighty Mice. Pony cars. Pimples on wheels. Or, courtesy of the University of Michigan's Office for the Study of Automotive Transportation, an august body notorious for its titular whoopee cushions: Entry-Level Upscale Coupes.

The Nissan NX2000 (designed, incidentally, by Nissan Design International at La Jolla) rests comfortably amid all this name-groping. It has two doors, a small bunk behind the rear seats for occasional inebriates and the whole stands knee-high to a hubcap.

At stop lights, it oozes the same level of aggression as an altar boy. But at the first flicker of green, this Nissan gnat will be two blocks up the street before the pack has cleared the intersection.

Do not try to follow it through traffic in your Chevrolet Caprice. Nor around entrance ramps displaying 25-m.p.h. warning signs.

You will make a wobbly, yawing impersonation of a Scud missile. The NX2000 will be half way to Encinitas.

At a base of $12,970, the little coupe is inexpensive. Gas mileage is a healthy 30-m.p.g. for a range of more than 300 miles between $10 fill-ups on regular unleaded.

Despite all this economy, the NX2000 is a superb runner and a grand handler with the added, sneaky delight of soundly outperforming the implication of its fairly routine looks.

The secret, of course, rests with the trickery that engineers are able to attach to small, four-cylinder engines these days. Those cylinders, for example, are made larger to create additional power from the firing sequence.

Instead of two valves, there are four valves per cylinder to allow better breathing and more efficient burning of the fuel-air mixture. Double-overhead cams--one for the bank of intake valves, one for the exhaust valves--make for higher engine revolutions and more power.

Add a lighter aluminum block and engine parts, a suspension stiffened by the addition of anti-roll bars, a chassis and its appendages tuned for more aggressive driving habits . . . and a small loss of driving comfort is replaced by a huge increase in performance pleasures.

There's also a distinct heightening of the potential for emotional exhilaration that to the mondaine among us has been known to surpass certain romantic activities involving Chanel and Champagne.

In short, the Nissan NX2000 clearly is a car for people with more sense than money.

The NX series is a replacement for the former Pulsar/NX line and its final abomination--modular styling, or quick changes to the rear bodywork by a variety of removable lids.

This blessedly ephemeral fad gave owners the choice of driving a notchback coupe, pickup truck, a Japanese El Camino, shooting brake, stakebed truck or mini-hearse for weekend work at the pet cemetery.

Far less than an idea before its time, modular styling was more an argument for notional bir h control.

Obviously, there is no such nonsense in Nissan's new NX lineup which comes in two versions: the NX1600 with a base price of $11,090 or the peppier and more expensive NX2000. Both have four-cylinder, 16-valve engines and double overhead cams. Both are available with manual or automatic transmissions, and driver-side air bags are standard.

But the 1600 has the smaller, 1.6-liter engine of 110 horsepower, while the 2000, as its numerals suggest, is a 2.0-liter engine delivering 140 horsepower. This is the same power plant used in Nissan's new Sentra SE and mini-Infiniti G20.

That's far from the end of the 2000's goodie list. The interior is softer and heavier with better fabrics. Brakes are four-wheel discs, with anti-lock brakes a $700 option. Fourteen-inch, seven-spoke cast alloy wheels are standard.

And the 2000 is available as a T-Top, quite the best compromise between claustrophobia in a coupe and hypothermia in a convertible.

Designers of the new NX like to emphasize its ovoid styling theme. The fog and headlights are elliptical. So are the door handles and taillights. Even the line of the roof and windows seems to form an oval swirl around the car.

No drastic exercise this. But it adds a certain identity and freshness to the car. We suspect that is all it was intended to do. It clearly is first kin to Nissan's mighty 300ZX and the unbelievably pretty 240SX sport coupe. The styling of neither car, it should be noted, lays an egg.

The only jar in the NX design comes with the very last thing you will see as the car departs--a chrome extension on the exhaust pipe. It looks after-market, thoroughly cheap, and like one of those mail-order $9.95 offers "to make your car sound just like an Italian sports car." It must go.

Internally, the NX1600 and NX2000 are pretty ordinary, which means pretty exemplary because today's imported interiors are a succession of optima.

Whether it be in an NX or a Honda Accord, these cars offer the best positioning of gearshift or length of shaft. Their instrument panels are empty of everything except pure purpose. Night does does not shadow their dials, nor sunshine obliterate them.

Their seats reflect as much attention to thigh and lumbar support as they do to back, butt and head rest. Turn signals precisely to the left fingertips. Windshield wipers exactly to the right. That little slab of a back seat folds down to serve the much higher purpose of usable cargo space.

So, whatever buyers have grown to expect from the insides of a modern car, they will find in the NX series.

The only problem on our test car was the hatchback trunk. It was a lump. Although hydraulically assisted, the balance was wildly out of whack and in drastic need of recalibrating.

Countering this, however, was a superb set to the doors.

Their pulls are a pistol grip extensions to molded arm rests. That automa tically makes opening the door a function of the fist and forearm. Doors with less thoughtful handles involve only the weaker linkage of one hand and a half-cocked wrist.

Earlier, we noted that the styling of the NX2000 is barely one bubble in a bloodline removed from the Nissan 300ZX.

The performance of the NX2000 is equally reminiscent of its sire. Not in top speed nor roaring away from rest, mind you. But certainly in polishing all the components of performance handling into an amalgam; allowing the merging of braking, shifting, steering and acceleration into a coordinated, single act.

Try that in many cars and you can be sure one piece of linkage will hesitate and one mechanical response will lag the rest until balance becomes no better than mildly ragged after a quick and unpredictable game of catch-up and compensation. With the NX, however, improved handling through constancy of manual and mechanical pressures appear to be an essence of the origin l design.

The gears are long-legged, shifting is a slick snick and the synchromesh is unbeatable. There is no high drama to braking from any speed o n just about every surface. And the steering is predictable and quite faithful on looser and faster curves.

We only wish that the exhaust note had been tuned to reflect any excellence of hand and footwork. Instead, you get a reedy rumble of tinny intestines.

The only other hang-up is that nadir of any front-wheel drive car with 140 horsepower pumped directly to the steering wheels: Torque steer.

In a straight line, the NX2000 is no problem.

But hammering out of a slow situation with wheels askew--particularly on less than putting green surfaces--there's enough skitter and forced steering to widen the eyes of the uninitiated.

In initial acceleration, the 2000 is quicker than the Honda CRX, the Volkswagen GTI and others in its class.

In mid-range acceleration--and in braking rapidly from applications of same--the 2000 is capable of taming and avoiding any freeway situation up to and including spinning semis.

Marketeers at the aforementioned and thigh-slapping Office for the Study of Automotive Transportation have cleanly defined target buyers of entry-level-upscale-sporty-subcompact-performance-specialty coupes.

They are recent college graduates who are marginally impoverished and don't require four seats in a car but still want a vehicle that reflects their freedom and energy.

For many it will be their first car.

For us old dodderers, theNX2000 certainly is light years removed from 1955 and the $400 Pontiacs of our sophomore years.

1991 Nissan NX2000

The Good Inexpensive to buy, economical to run. Smallsize, high performance, optimum handling. Ample room even for little Lakers. Speaks of individuality.

The Bad Wimpy exhaust note. Twitchy torque steer. Unwieldy trunk.

The Ugly Chrome-tipped exhaust.

Cost Base $12,970 As tested $15,420 (including T-Top, anti-lock brakes, air conditioning and driver-side air bag)

Engine Four cylinders,16-valve, 2.0 liters developing 140 horsepower.

Type Front-wheel drive, two-door, 2+2, performance sport coupe.

Performance 0-60 m.p.h., as tested, 8.3 seconds. Top speed (estimated), 125 m.p.h. plus. Fuel economy, EPA city-highway, 23 and 31 m.p.g., with 5-speed manual transmission

Curb Weight 2,516 pounds (with T-Top).