ABOARD THE MOTOR VESSEL BERNARD G. - The muddy Mississippi bends gently westward around the sleeping town of Hickman, Ky., and the two huge diesels driving this towboat throttle down to take the turn. In the ensuing silence, a passenger can almost hear Huckleberry Finn out there somewhere on his raftt, carrying on even now about "the goldurndestriver a body ever see."

For the Mississippi today seems, at first glance, to be the same natural wonder that won the heart of Huck Finn.

Boats like the Bernard G., pushing long strings of barges upstream and down, can go hours without sighting a village, whole days without passing under a bridge. For long stretches, the mile-wide river is flanked by nothing but virgin forests and high sand bluffs.

Closer examination reveals, however, that the Father of Waters is no longer Mark Twain's "magnificent untamed torrent." Forty years of damming, diking and dredging by the U.S. Army Corps. of Engineers have harnessed the great river, making it a reliable, predictable, predictable highway for the barge lines that move enormous quantities of grain, chemicals and fuel between Minneapolis and New Orleans.

The considerable expense of the federal government's waterway work - more than $1 billion annually, according to the Department of Transportation - and the competitive advantage it has given the barge lines over truck and rail freight companies have prompted repeated efforts in Congress to make the barge industry pay a fee for using federally built and maintained inland waterways.

This year, for the first time, the Senate has passed a waterway fee bill - $790 - and the House seems likely to follow suit.

In Washington, that development has been viewed as a parliamentary and political coup for backers of the bill. Out here on the river, though, $790 is a dagger in the back.

As the bargemen see it, a Congress that has always been generous in funding water projects has suddenly changed the rules.

"The politicans don't understand," says Bob Gardner, who serves as commodore of the towboat fleet maintained by the Alter Co. of Davenport, Iowa.

"For years we've been doing a job out here - hauling grain - and we don't do it bad when people leave us alone. This year, all of a sudden, we're in this political volleyball game with a bunch of people who don't understand the river or our business."

To try to understand the river and the booming freight business it supports, I rode down the Mississippi recently aboard the Bernard G., one of Alter Co.'s six towboats.

The Bernard G. (the name was the brainchild of Alter's president, Bernard Goldstein) is painted gleaming white with yellow trim, and looks like a four-tiered rectangular wedding cake, with a forest of antennas sprouting from the top layer.

She is 145 feet long and 40 feet wide, about average for Mississippi towboats. Her draft is only nine feet - any more and she could not get through the 29 locks the Corps of Engineers operates along the river.

The top tier of this floating cake is the "pilot house" - what a seagoing sailor would call the "bridge." Beneath it are three more enclosed structures, each slightly larger than the one above, housing crew and guest quarters, a galley and dining room and various storage lockers.

The lowest deck is essentially one big engine room, holding the two thurdering Detroit Diesel engines that send a never-ending shudder through the spine of the boat (at full power, the crewmen's coffee vibrates right out of the cups.)

The diesels' 5,600 horsepower make the Bernard G. one of the most overpowered 145-footers that ever took to water. But of course, the power is not for the towboat; it is there to push the load.

Terminology is backward here. Although the riverboats are called "towboats," they don't tow. They push the barges ahead of them.But the nest of barges that is pushed is called the "tow."

To the crew of the Bernard G., the tow assembled for the downriver trip I took was smaller than normal: to this newcomer, it was predigious. Each barge is roughly the size of a three-story, 10-unit department building. Our tow consisted of 21 of them strung together in a four-by-five block (with the extra barge out front) thhat covered five acres of river.

The barges were grain hoppers, for the most part, but there were some molasses and tallow tanks along as well. In total, Bernard G. was pushing about 30,000 tons of freight on this one trip: it would take six 100-car trains to move as much. Like most riverborne grain, the cargo was destined for New Orleans and rendezvous with a Europebound freighter.

The barges are bound tightly together by iron cobwebs of 1 1/2-inch cable wound in intricate networks around each corner of each barge. A separate set of cables, their tautness maintained by winches, ties the tow to the front of the Bernard G.

The ties that bind the barges will burst if bound too lightly, or give way if not held taut enough. To guarrd against either, deckhands are roaming about the tow all the time, kicking and pulling at the lines in the same boatman's ballet that Huck Finn watched at night from his raft.

Four decks above the tow, the Bernard G.'s pilot house looks more like something from Star Wars than fromm Mark Twain.

Dials glow, warning lights blink. The pilot sits between two large radar screens. He scans the digital readout from two sonar units that read the river's depth. He steers not with the classic multi-spoked wooden wheel, but with a stainless steel tiller linnked by hydraulic drive to the rudders astern. Bay windows on all four sides provide a 300-degree view of the river.

The Bernard G.'s two drivers, Capt. Ken Baiin and Pilot John McNeil, who inhabit the pilot house in alternating six-hour shifts, reflect two sharply different styles of piloting.

McNeil, a perfect country gentleman from Greenville, Miss, is the tortoise. When the chart shows a sharp curve coming, he will cut the engines a half-mile upstream, letting the current carry boat and tow gently through the turn.

Bain, a hotrodder from Savannah, Tenn., prefers to barrel into the turns at full speed (about 11 miles per hour), wrenching the pneummmatic throttle from "full ahead" to "full astern" to keep the unwieldy train of barges from piling over a bank or sand bar.

Under either man, though, the pilot house has an air of easy nonchalance, like a suburban family out for a Sunday drive. The difference is that this football fields jutting out beyond the windshield.

Where the river is wide and the curves easy, it seems simple enough to keep the long tow in line. Around the sharp bends, though, driving a riverboat is like pushing the Washington Monument up the Rock Creek Parkway ahed of the family station wagon - with no brakes.

The federal government's multibillion-dollar investment in the waterways helps make that feat possible.

At almost every turn the Army has put in a dike or jetty to direct the current and keep boats in midstream. A fleet of workboats is continually dredging a passable channel along the shifting river bottom. To mark the channel, the Coast Guard maintains lights and buoys every quarter-mile or so along the Mississippi's 1,000-mile course.

In making the river safe, the government has created a new danger: traffic. Freight movement on the inland waterways has skyrocketed in the past two decades: today 16 per cent of the nation's freight moves by water. As a result, the Bernard G. is almost never out of sight of another boat and tow.

To avoid collisions, the river pilots are constantly on their radios. They let the boats ahead know they are coming, and inform those behind of what's in store. They create ad hoc rules of the road for each passing:

"I'm coming up along the bend at Sickman. Cap'n. Which side you want to take?"

"Don't make no never mind to me. Cap'n. Why don't you stay on that Kentucky bank and I'll take her over to the Missouri side?"

"Sounds good. Cap'n. Now you got two more good-size tows coming right after me."

The casual chatter of the air waves makes the whole river seem like a big family, and in some ways it is. The boatmen almost all share the same Southern country upbringing: they are common stock in a common business, and they all seem to feel an affinity for every boat and crewmen on the river.

The sense of family is emphasized within the crew of Bernard G., who live together on the little boat for 30 days at a time or more. Although the boat is regularly in such ports as St. Louis or New Orleans, the crewmen get no liberty. Bernard G. stops only for the few hours needed to drop one two and pick up another.

In a port or on the river, a crewman works seven days per week, two six-hour shifts each day.

Each six-hour watch includes a driver (either Bain or McNeil), an engineer to watch the diesels, and three deckhands working the tow. The 11th crew member the only woman aboard, is the boat's cook, nurse and den mother, Janie Devers, a Tennessee belle who serves up at each change of watch a gargantuan and delicious banquet of country food.

A boatman generally works 30 days on the boat and then takes 15 or 20 days off, so he is actually on the job only seven to nine months of the year. For that, a beginning deckhand can expect to earn $9,000 to $11,000 annually. A captain's pay will approach $30,000.

The work is exhausting, even for the brawny rivermen, and when a six-hour watch is done the men of Bernard G. sit in Janie's air-conditioned galley for an hour or more, sipping Dr. Pepper and regaining their strength.

The talk around the galley table is half river jargon and half country stories about the farms back home.

Bain is a constant topic, for he apparently drives even less delicately ashore than he does in Bernard G.'s pilot house.

"I remember the week he cracked up his wife's car one day and his own the next," chuckles engineer James Porter in his easy drawl. "Then he goes and rents another, and damn if that one doesn't end up a wreck too."

The boatmen are in independent breed, distrustful of big business and big government in equal proportions, and ther is rarely any talk of politics. This year, though, $790 is changing that.

On the bulletin board above the color television in the crew's lounge is a letter from a barge industry lobbyist, seeking contributions for the political battle back in Washington. That has started the crewmen thinking, and they all have their views about the waterway fee.

"Maybe I'll surprise you," says deckhand Phil Little, "but I think they ought to pass it. The government's got a lot of money in this river. If the truckers have to pay, why don't we?"

In the pilot house, John McNeil demurs.

"It's like you go over here to some little stream," he says, "and catch you a mess of fish. Then that fellow come up and says, you got to pay me for those catfish. It's not right.

"it ain't the idea of paying the $3. It's the idea of paying for a river. It's not right."