Nissan has vowed to shed its conservative image in 1989. A remake of the old 200SX economy car into the 240SX sports coupe is good for starters.

The 200SX was a high-mileage subcompact posing as a sports model. Such a guise led to the undoing of the Pontiac Fiero and Ford EXP, handsome machines whose power never matched their looks.

The old 200SX coupe appealed to youthful drivers who wanted to be seen in a sporty looking car that didn`t act intimidating. Owners primarily were concerned with 20 miles per gallon, even if the 0-to-60 time was measured by sundial.

The SX coupe has been resized, restyled and renamed the 240. The number refers in part to the peppy 2.4-liter, 12-valve, 140-horsepower, 4-cylinder engine. It also is a psychological maneuver aimed at associating the SX with the original 240Z sports model that proved so successful and moved Nissan into the major leagues.

The 2.4-liter 4-cylinder has 40 horsepower more than last year`s 2-liter 4-cylinder in the SX. You sprint from the light. But an even more influential test of an engine is what happens when you`re traveling down the roadway, come upon a steep incline-common along the Int. Hwy. 94 route between Chicago and Detroit-and press the pedal while in fifth gear.

In the 240SX you accelerate without having to downshift to fourth or third gear and then upshift again. Good power in reserve. The 240SX claims 0- to-60 m.p.h. in 8.8 seconds.

The real beauty with the 240SX, however, is the ride and handling. Though the majority of new cars are front-wheel drive, Nissan stuck with rear drive in the 240SX, saying it provided better weight distribution, especially in high-speed driving.

The 240SX has above-average road-holding manners. Tight, crisp turns and corners without body roll or sway are the rule. The 15-inch steel-belted radial tires stuck to the pavement with the silent help of the computer- designed, 5-link independent rear suspension.

With the power-assisted rack-and-pinion steering, you need only a little effort on the wheel to point the nose in the direction you want and have it respond quickly. The thick steering wheel contributes to the feeling of control.

The 240SX comes with four-wheel disc brakes. But one major disappointment is that antilock brakes are a very costly option, at $1,400, and will be offered on the SE fastback only, starting in November.

That $1,400 puts the system`s ability to stop a car in a straight line regardless of road surface out of reach of most consumers. If you can amortize $1,400 over 36, 48 or 60 payments, do so. We`d prefer that Nissan brought the price more in reach of the masses, rather than have the masses have to reach to enjoy the option.

For 1989, the 240SX comes in two versions: fastback with a sharply sloping gl ass hatchback lid, and notchback, with a more formal standup rear roof line. We drove the fastback.

Both versions are built on a 97.4-inch wheelbase and are 178 inches long, which compares with a 95.5-inch wheelbase and 174.4-inch length on the 200SX in 1988.

Up front, body-colored wraparound bumpers, concealed headlamps and an air dam grab attention. In back, the wraparound body-colored bumpers and deck lid spoiler burnish the sporty look.

The 240SX is one heck of a package, but that`s not to say the car is without faults. It has some glaring problems and annoyances, some of which are brought about by the styling.

The slope of the roof and hatch lid on the fastback not only rob the driver of some rear vision, but it also makes it impossible for an adult to sit in the back seat. To carry an adult in back, you must ensure that he or she is lying in the fetal position. Little kids, okay; teens a squeeze; adults an absurdity. Ironically, a rear seat ashtray is standard.

The rear seat backs fold down to allow more cargo capacity, which i s really all that should go behind front seat occupants if you opt for the fastback.

Up front, there`s plenty of room. To ensure a supply of space, the armrests in the doors sweep away from the driver and occupant. Great touch, but one that`s spoiled by placing map pockets under the armrests that sweep inward toward the driver. Reach down along the seat for the adjustments and you put your hand in the map pockets.

The 240SX comes with a fuel filler door release knob to the left and under the driver`s seat. The knob repeatedly wouldn`t open the door. The lug wrench had to be used to pry it open.

Another gripe is that the heavy hood is held up with a metal prop rod rather than a spring, not a confidence builder for do-it-yourselfers.

On the positive side, the front bucket seats not only are wide, but they also have side bolsters that sweep out along occupants` torsos. That makes for comfortable long-distance driving as well as keeping driver and occupant in place in sharp corners and turns.

The 240SX also comes with automatic belts that fasten around your upper torso after you are seated and turn on the key; the belts pull away when the key is turned off and the door is opened. The belt is snug but not tight and doesn`t droop after several miles of driving. Nice touch.

Positioning of controls is good, too. Rear-window wiper/washer/defroster are in easy sight and reach on either side of the steering wheel. The cruise control hardware is dash-mounted and about the easiest to use that we`ve come across.

Base price on the fastback is $13,199, and on the notchback $12,999.

If the 240 is any indication of what we can expect with the new 300ZX coming out next spring after a Chicago Auto Show debut, Nissan`s boast about image will prove prophetic.

Also coming from Nissan for 1989 is the bigger and newly styled Maxima and the Axxess mini-van, with front-wheel and four-wheel drive. Should be a good year for Nissan.

Among the other changes at Nissan for 1989, the subcompact Sentra and Pulsar sport a 1.6-liter, 12-valve 4-cylinder that boasts 90 horsepower versus 70 in 1988. The Stanza has subtle styling changes, including a new grille, wheel covers and bodyside moldings. Nissan will continue to sell the 300ZX as a 1989 model until the new version comes out in the spring as a `90. In the utility end, Pathfinder adds a two-wheel-drive version in January to the four-wheel-drive model.