They laughed in 1946 when Sen. John L. McClellan (D-Ark.) talked about building a port in this land-locked city 400 miles from the sea. Today, the only ones laughing are the stevedores who earn $7.88 an hour unloading Japanese steel at the foreign trade zone maintained by the Little Rock Port Authority.

Thirty years and $1.2 billion in federal money have transformed the Arkansas River from a serpentine gulch of sandbars and mudbanks to a shimmering blue freight way connecting Little Rock (and Tulsa, 300 miles upstream) with the sea.

The development of the river has been a factor - but not the only one - in a major economic reversal in the Arkansas basin that has turned the dusty agricultural states of Arkansas and Oklahoma into bustling center of industry.

Now Congress is threatening to tkae away at least part of the bounty the river project has brought.

For this is where the waterway toll bill, S. 790, would pinch.

S. 790 which passed the Senate in June and should emerge in some form from the House this month, would force commercial barge lines to pay a toll for using federally maintained inland waterways such as the Arkansas. That could seriously limit the Arkansas River's economic utility. Without the free right of way, bargement here could bot set their rates low enough to compete with truck and rail shippers.

A study by the Congressional Budget Office predicted that the Senate-passed bill would eliminate 96 per cnet of the Arkansas' freight traffic. The bill's sponsor> Sen. Pete Domenici (R-N.M.), says the impact would be far less.

For waterway boosters here, S. 790 looms as a death warrant.

"It would kill the goose that laid the golden egg, as far as we're concerned," said Wallace Gieringer, director of the Port Authority at Pine Bluff, 40 miles downstream from Little Rock.

"We're getting more and more development along the river, but we haven't even been open for naviagation for 10 years yet. This system is too young to survive a blow like that Domenici bill."

If the river were to dry up economically, because of the legislation, it is not clear how seriously the region's overall economy would be affected. Some locl aplanners suggest the impact would not be fatal.

"The river is a tool, I say, one tool, in our kit for attracting industry here," said Windell Adams of the Arkansas Industrial Development Commission.

"We'd hate to lose it. But we have some excellent rail lines here, we have interstates. Most of the economic revival here began before they built the river."

Congress authorized the Army Corps of Engineers to "build the river" in 1946, but construction did not begin until 1957.

The Army spent 15 years on the job, which it proudly labeled "the largest civil works project in history."

To provide a navigable channel all the way to Tulso, the Army put in 17 dams, each requiring a lock to permit boat passage. Where a river's oxbow turns were too sharp for barge traffic, the Army simply tunneled through the earth to build a new, straight river.

On completion in 1971, the Arkansas project was hailed as a triumph of man's reshaping of nature. It became the model for a host of other huge projects, including the Tennessee-Tombigbee waterway under construction in Mississippi.

To celebrate completion of the project, Army engineers prepared an official history of the river.

"For more centuries than man can count," the history notes disapprovingly, "the Arkansas River was left to its own devices . . . Now the Arkansas works for mankind."

Barge traffic moving downstream carries coal, ore and agricultural products to ports along the Mississippi.

Coming up to Little Rock and Tulsa are steel and other industrial materials and various forms of fuel, incluidng diesel fuel for the Missouri Pacific Railroad, the waterway's arch competitor.

In a classic instance of carrying coals to Newcastle, the barges also are bringing bauxite to Bauxite Ark.

Bauxite was the site of America's only significant deposits of the powdery red ore, the principal source of aluminium. The locl amines are almost depleted, and so the ALcoa and Reynolds Aluminium Co. plants here are bringing in bauxite from Jamaica and Venezuela.

In addition to the commercial traffic, the river project has been a boon to recreational boaters, creating a chain of placid lakes and eliminating the seasonal changes that used to turn the best fishing holes into sandbars during the dry months.

The recreational craft move through the 17 locks just as the barge boats do, without paying any transit fee.

A 14-foot rowboat can pull into a $100 million lock anytime, and the eight-person Corps of Engineers lock crew will move 27 million gallons of water, free, to let the fisherman rise over the dam and go on his way.

The fear among waterway proponents here is that, if a harsh waterway fee bill is passed, the fishermen in their 14-footers will be the only people still using the $1.2 billion river the Armey created.

"We're all proud of the river project and what Sen. McClellan got for us here," said James C. Oliver, a Little Rock freight broker who deals with all modes of transit.

"But nobody is moving things by water because of the romance of the river. It's just cheaper. If some bill passes that raises rates on the river, all that barge freight is going to move some other way."