For weeks the Washington lobbyists for the waterways industry had anxiously scanned each day's Congressional Record looking for their resolution. Finally, last Tuesday, there it was.

On April 25 Sen. Russell Long (D-La.) introduced a Senate resolution calling for a "detailed study" of "numerous unanswered questions" relating to federal support for commercial transportation.

Neither Long's resolution nor his prepared remarks about it mentioned Sen. Pete Domenici (R-N.M.) or Domenici's bill, S.790, which would require barge lines that transport freight on the nation's inland water-ways to helps the government pay for maintaining those waterways.

But Long's resolution was an arrow armed at the heart of S.790.

For one thing, the soft spoken senator from Louisiana wasn't thingking of any short-term study: his resolution specifically called for 24 months of investigation. In Congress, where "let's study it" is a standard euphemism for "let's kill it," that resolution would be the kiss of death for Domenicis' bill for at least two years.

And Long who is probably the Senate's strongest opponent of any waterway charge had conveniently resolved that the study should be carried out by the Senate Finance Committee - a committee chaired by Russell Long himself.

For the waterway lobbyists, Long resolution was perfect. They couldn't have been happier if they had written it themselves.

In fact, to a large extent they had.

It was back in September, 1976, when Domenici first started talking about a toll system on the waterways that Washington representatives of the major barge lines and their chief customers had come up with the "study" strategy.

"There was quite a group of us that worked on it," recalls Jim Smith, president of American Waterways Operators, an industry association. "We were on it and the National Waterways Conference and some others.

"Sen Long's staff had some input into the language of the thing too," Smith said.

An official at another industry association said he attended several sessions last fall in Long's office to work on the resolution.

For the most part, he said Long was too busy to attend instead, the work was directed by Herbert R. Harr Jr., a New Orleans port official who was then chairman of the National Waterways Conference, an umbrella group of shippers, barge lines, and local waterways authorities.

Long said in an interview that he had asked his staff to prepare the resolution. "But of course you always want to refer something like that to the people who are going to be affected," he said with a gentle grin.

All this spring, while Domenici's bill was picking up support from this economist and that senator, the waterways people bit their nails waiting for the resolution to appear. They could hardly start lobbying for its passage after all, until Long got around to introducing it.

For Domenici and his staff, the Long resolution was demoralizing but not entirely unexpected.

In February, when he introduced S.790. Domenici had manuevered adroitly to keep the bill out of Long's committees. But he knew that no money bill could long escape Russell Long.

"Of course I knew that Sen. Long was going to have something to say on the issue," Domenici said after he read the resolution. "And I knew he thought the Finance Commitee was the right place for it.

"But the resolution for a study of all transportation came as a surprise to me. I thought at least we might get a [waterway toll] moving this year."

Still, there were grounds for maintaining stiff upper lips to the Domenici camp.

"It's one thing to put in a resolution," said Hal Brayman, of Domenici's staff. "It's another to pass it - even if you're a committee charman. I think a lot of senators will under stand pretty well what this study was designed to do."

Moreover Brayman noted there is one person in Washington this spring who has at least as much influence with Congress as Russell Long does - Jimmy Carter.

"The most important things for the user charger bill right now is what the administration says," Brayman added. "If they come down here and say the nations needs the income from waterway fees and needs it now, I don't think many people will want to wait for a two year study.

But will the administration say that." Two weeks ago in his message to Congress on water project. Carter had come out in favor of waterway tolls. But would he be willing to fight Russell Long head-to-head to get them?

Those questions may be answered in a hearing this afternoon, when the Carter administration finally tells the Senate what it think about S.790.