What the buyers of light-medium-,and heavy-duty trucks want is more roominess and power, with less downtime for service and repairs. And that's what manufacturers are rolling out for 1998.

Cabs are getting bigger everything from pickup trucks to trailer-hauling tractors, some of which have sleepers spacious enough to be outfitted like luxury motor homes. Makers of light-duty pickups are rushing to market with third or fourth doors to make the back seats of their extended cabs more accessible.

In the sport-utility-vehicle (SUV) segment, truck makers are going to great lengths. The king-of-the-road Chevrolet and GMC Suburbans, the longest SUVs ever built at 219 inches, may be outdone soon by a Ford "crew wagon" that is 10 inches longer.

Demands for power are satisfied by muscle as makers of light-duty trucks offer bigger engines or tweak engines to produce more horsepower. For the first time, a V-8 is an option on a compact SUV, the Dodge Durango. In the heavy-duty-truck segment, there are the Arnold Schwarzeneggers of diesel engines: the Cummins Signature 600 and the Caterpillar 3406E, both achieving 600 horsepower.

Less Wasted Time

For protection against costly downtime, some manufacturers are offering buyers more help if their vehicles go out of service. Chevrolet, for example, offers light-duty-truck owners 24-hour roadside assistance, and the company will provide a free rental vehicle if overnight repairs are needed during warranty-covered work.

Kenworth is finding that most buyers of its new T2000, a truck in Class 8 (more than 33,000 pounds gross vehicle weight, or GVW), are opting for the Extended Service Interval maintenance program. The service interval under this option is every 25,000 miles instead of the industry norm of 10,000 to 15,000 miles; the engine is guaranteed against repairs that might be needed because of the longer interval.

For 1998 models, most prices are holding steady. Chrysler announced in mid-August that its prices for 1998 cars and trucks will drop an average of 0.6 percent; Ford plans no price increases; and General Motors has said that prices for cars and light-duty trucks will rise an average of 1.3 percent.

Trucks, including mediums and heavies, made up 44.8 percent of total vehicle sales in 1996. For 1997, through July, trucks were up to 45.9 percent of the total market, according to GM spokeswoman Annemarie Sylvester.

Sport-utilities accounted for 12.6 percent of industrywide sales for the first seven months of 1996. For the same period in 1997, they grew to 14.7 percent of sales.

Pickup sales have been down slightly. Minivan sales have been flat, partly because baby boomers are maturing beyond the need for a "family shuttle bus," says Jay Houghton, director of marketing at A.T. Kearney, Inc., an automotive consulting firm in Southfield, Mich.

Alternative Fuels

Manufacturers of light-duty vehicles are getting serious about alternative fuels. Chrysler and Ford have announced plans to produce dual-fuel vehicles that can operate on gasoline or on E-85, a mix of 85 percent ethanol and 15 percent gasoline. The companies are motivated by a federal law that lowers fuel-economy standards by as much as 1.2 miles per gallon for vehicles that can run on either ethanol or gas.

Because of safety concerns air bags, buyers of most pickup trucks that lack rear seats now can push a switch that disables the passenger-side bag temporarily if a child or small adult is riding in that seat. Several truck makers are producing gentler-inflating air bags to reduce the risk of injury to children and small adults in front passenger seats.

In the heavy-duty segment, truckload carriers' business is booming, and the Class 8s are surprising experts who had forecast that sales of the big trucks for 1997 would be less than last year's 170,000 units.

"A lot of freight is moving. There's a reasonable probability that sales in 1997 could be 10 percent more than last year," says Stuart MacKay, owner of MacKay and Co. in Lombard, Ill., a consulting firm for the heavy-equipment industry.

Light-Duty Trucks

Following are new trucks and features in Class 1, up to 6,000 pounds GVW; Class 2, 6,001 to 10,000 pounds; and Class 3, 10,001 to 14,000 pounds.

Acura

The SLX sport-utility's new, more-powerful 3.5-liter V-6 combines with what Acura calls "torque-on-demand," which transfers power to all four wheels at the touch of a button. The SLX has a redesigned front end and new luxury items, including power fold-in side mirrors and heated power front seats.

AM General

AM General makes few year-to-year changes to the military-born Hummer, whose commercial applications include construction, mining, oil exploration, and forest. An optional turbo diesel engine, a 6.5-liter V-8. has been upgraded from 190 to 195 horsepower.

Chevrolet

Businesses now can buy the nimble-handling Chevrolet Venture as a cargo wagon, adapted from the popular minivan that arrived as a 1997 model. The cargo version can be ordered with sliding doors on one or both sides and is available on extended wheelbases only. Cargo space stretches up to 155.9 cubic feet for four-door models, and the van can carry payloads of up to 1,519 pounds.

The S-10 compact pickup has undergone front-end changes that make it more closely resemble Chevy's big C/K pickup. Chevrolet's gold bow-tie logo now appears on the small sport-utility that is now called the Chevrolet -- not Geo -- Tracker.

This past spring, GM began production on optional dual-fuel versions of the two-wheel-drive, regular-cab, full-size Chevrolet C2500 and GMC Sierra pickups. Their Vortec 5700 V-8 engines operate either on gasoline or compressed natural gas.

The G3500 van makes standard the Passlock theft-deterrent system, which prevents the engine from starting for 10 minutes if a wrong key is used. Improvements have been made to both the regular and the heavy-duty four-speed automatic transmissions with overdrive.

Chrysler

The newest Chrysler Town and Country is a luxury suite on wheels with comfort assists including optional heated front seats and increased power from a 3.8-liter V-6.

All three minivans produced by Chrysler Corp. -- the Town and Country, the Dodge Caravan, and the Plymouth Voyager -- are offered with flexible-fuel engines that run on either gas or E-85. The Plymouth Grand Voyager Expresso has a package that includes remote keyless entry and special nameplates.

Dodge

The Durango, Dodge's first sport-utility vehicle, measures more than a foot longer than the longest Jeep, making it the largest compact-size SUV. Dodge says the Durango is the only compact sport-utility with optional eight-passenger seating.

At the top of the Durango's three Magnum engine choices is the powerful 5.9-liter V-8 with 250 horsepower; it's the only V-8 in the compact sport-utility segment.

The nice-handling, full-size Ram Quad Cab is the first pickup to offer dual access doors to the rear seat.

Ford

The compact-size Ranger pickup gets a new front end reminiscent of the popular Explorer sport-utility A new 2.5-liter four-cylinder engine replaces the previous 2.3-liter, and suspension changes have improved handling. The engine operates quietly and accelerates efficiently.

A longer wheelbase on the regular-cab Ranger gives 3 more inches of legroom and 4 extra cubic feet of interior space. The Ranger is expected to get a four-door option during the 1998 model year.

GMC

The Jimmy, a compact sport-utility vehicle, and the Sonoma compact-size pickup get new front-end styling plus added seating comfort and instrument-panel improvements. Both vehicles have GMC's Truck Body Controller, computer-based electronics that perform tasks such as automatically turning on and off and dimming headlights and disabling the fuel system for 10 minutes if someone tries to force a lock.

Modifications have increased brake life and decreased stopping distances on both vehicles. A new trailer-hitch configuration configuration has raised towing capacity from 2,000 pounds to 3,500 pounds.

Honda

The successful CR-V sport-utility, introduced in February, will add new models next February.

The updated four-door Passport sport-utility, twin to the Isuzu Rodeo, has an all-new exterior with a roof rack and heated dual power mirrors as standard equipment. Roominess and seat-down cargo volume have been increased.

The Passport still has a 3.2-liter V-6 engine, but horsepower has been increased to 205 from 190.

Infiniti

The QX4 luxury sport-utility, based on the Nissan Pathfinder, was new for 1997. Its All-Mode system acts like two-wheel drive on dry roads. But if the road becomes slippery, the QX4 automatically shifts -- so smoothly that it's undetected by the driver -- to a 50-50 split between front and rear wheels.

Isuzu