IT NOW APPEARS that Congress, at long last, is going to impose a user charge on the barges that ply the inland waterways. Even the barge companies, after fighting the idea for more than 35 years, seem reconciled to the fact that he votes needed to pass the legislation are there. So it is not surprising that the struggle has shifted to the question of what kind of charges there will be.

The bill passed by the Senate two months ago seems to us to have been on the right track. It would direct the Department of Transportation to devise a system of tolls and fees for the use of the waterways. These would increase gradually until they were high enough to pay some of the costs of constructing the facilities the barge companies use as well as paying for the maintenance and operation of the system. This bill rested on two important premises. One was that the charges paid by each barge company should be related to the cost of supplying the particular facilities it happened to use. The other was that the constant pressure for expansion and improvement of the waterways would be reduced if part of the construction costs came out of the pockets of those who now apply most of the pressure.

Unfortunately, the House Ways and Means Committee has now abandoned both of the ideas that lay behind the Senate bill. Its version of the barge bill would simply impose a tax of 6 cents a gallon on the diesel fuel used on the waterways. While this approach does spread across the barge industry the burden of paying for the waterways, it eliminates the idea that each company should pay part of the costs of the facilities it uses. Instead, each company's payments would be based on its fuel usage. Much of the barge industry finds the tax more palatable than the toll arrangement, particularly the part that uses the Columbia River and transport farm products out of the congressional district represented by Al Ullman, the Ways and Means Committee chairman.

While there may be some merit in the tax approach adopted by the House committee - trucking companies pay their share of the interstate highway system that way - the level at which the tax was set destroys the rest of the rationale underlying the Senate version. At 6 cents a gallon - and the House committee gave no indication it expected that rate to increase - the revenue generated will never cover the government's maintenance and operating costs, let alone begin to pay part of the costs of construction. Indeed, the estimates are that the fuel tax would have to reach 40 cents a gallon to match the eventual tolls proposed by the Senate. That means the pressure for more locks and dams will continue unabated, since the construction of them would bear no relationship to the user charges paid by the barge companies. We would prefer the Senate's approach, while conceding that the House version is better than nothing - which is all the Congress has been willing to do in the past for the eight Presidents who asked for user charges of this kind.