A plan to save American consumers as much as $4 billion a year while reducing traffic congestion, fuel consumption and air pollution has been targeted for defeat by the railroads and their front-group - Citizens for Reliable and Safe Highways.

The plan calls for the limited introduction of more productive trucks - longer combination vehicles (LCVs) - on the interstate highway system and other designated routes as determined by the needs of individual states.Contrary to claims made by the rails, the trucking industry is not seeking nationwide access for these LCVs.

Instead, the American Trucking Associations will propose that Congress include in highway legislation next year a provision to allow all the states to determine their own rules on LCVs.

Today 15 states allow trucking companies to buy permits to operate LCVs - triple-trailer units and turnpike doubles (two 48-foot trailers.)

Estimates by the trucking associations note LCVs could haul nearly 4 percent more ton-miles of freight while traveling 3 percent fewer miles.

In this way, LCVs can reduce congestion and pollution. Triple-trailer units move a third more freight than double trailers and roughly 50 percent more than a typical tractor-semitrailer, with virtually no increase in air pollution and at fuel savings of 27 percent to 40 percent.

The benefits of LCVs - they have been safely operating in the western United States for 30 years - have been noted in a congressionally mandated study from the National Academy of Sciences and two follow-up studies by the Trucking Research Institute of the ATA Foundation.

Although LCVs will be heavier than the ordinary federal 80,000-pound gross vehicle weight limit, these vehicles will actually be easier on highways because they will use more axles. Since pavement wear is a function of axle weight, LCVs will spread more weight over more axles. ATA does not seek to raise axle weights.

Rational argument against the widespread productivity benefits of LCVs would be difficult. This explains why the rails and their allies are spending millions on scare tactics to convince motorists to join them in sidetracking LCVs.

Not only is the safety record of LCVs better than that of single-tractor-semitrailer combinations - nine deaths in accidents involving triples in the past decade and only four from all LCVs in 1988 - it is important to realize that LCVs will be used only on a limited basis.

The public will not see LCVs in downtown city traffic. Only a limited number of trucking companies will use LCVs and then only under safe road conditions using only the best drivers.

The argument by railroads and CRASH that LCVs are unsafe and a danger to motorists is untrue and cannot be documented.

So what are the railroads really afraid of? Railroads fear a loss of freight to more efficient trucks. The truth is, only about 5 percent of rail freight would be diverted to LCVs. A larger amount of LCV freight would be diverted from less productive trucks. It appears the rails do not want to compete in the marketplace with more-productive trucks.

In short, there is much to benefit America's economy and little, if indeed anything, to lose by allowing LCVs under a nationwide permit system controlled and operated by the states under limited federal regulation.

ATA expects Congress to be highly interested in these benefits.

(Thomas J. Donohue is president of the American Trucking Associations.)