Picture this in flickering black and white, run at Keystone Kops pace:

A work train stops in the middle of a long railroad bridge. Eighteen men get off and start frantically pulling spikes, taking up rails and moving overhead electrical lines.

Suddenly, the middle span rises. It's a drawbridge. Six yachts, waiting in the river below, go through. The bridge is lowered. The electrical wires and tracks are replaced. The 18 men climb on the train. The train leaves. All done in 45 minutes.

It cost Amtrak $4,000 to do that four times every summer weekend on the Bush River Bridge near here.

The cost of repairing the existing draw mechanism and putting in the rails and overhead electrical wires that would permit automatic, one-man operation is estimated by the Federal Railroad Administration at $41,962, or 10 summer weekends plus a Saturday.

Both Amtrak and Leo Sullivan, attorney for the Bush River Yacht Club, think this situation is ridiculous, but for very different reasons.

Amtrak inherited the bridge and the tracks on it dring the reorganization of the northeastern railroads. The Bush River Bridge is just one of many between Washington and Boston that must be repaired before Amtrak can do what it is charged by Congress to do by 1981: run passenger trains at 120 m.p.h. and cut the New York to Washington trip to 2 hours, 40 minutes.

Draw spans and the kind of rails they require are not compatible with 120 m.p.h. speed. "We'd have to slow down to 70 or 80 m.p.h. to cross the bridge," said Robert F. Lawson, assistant vice president and chief engineer for Amtrak. Amtrak has petitioned the Coast Guard to close the span permanently and end the weekend stillness.

Sullivan, 67, is one of the founders of the Bush River Yacht Club as well as its lawyer. He has spent much of his adult life fighting to keep the Bush River Bridge open. First it was the Pennsylvania Railroad, then the reorganized Penn-Central, now Amtrak. But the issue has always been the same: access for large boats to the Chesapeake Bay beyond the bridge.

Under the current agreement, the bridge is opened twice on Saturdays and twice on Sundays between June 1 and Sept. 30, but only if 24-hours' notice is given to the railroad.

The bridge, built in 1912, was opened on demand until World War II, when it and many other similar draw spans were closed. Modifications to the rails on the bridge and to the draw mechanism were made during the war by the Pennsylvania Railroad without formal approval of either the Coast Guard or the Army Corps of Engineers, according to a 1972 Coast Guard report. Itis because of those modifications that an 18-man track gang is required to open and close the span today.

The Bush River Yacht Club, one of the three behind the bridge, is located picturesquely on the shores of the Bush River in Hartford County. From the clubroom the half-mile-long bridge is clearly visible.

Sullivan and Rebecca Ratterhoff, another longtime club member, explaind their grievances. "The word, rights, today means nothing," Ritterhoff said. "We're paying for every railroad ticket that's bought, and runs at an enormous deficit - about $515 million in the fiscal year just ended - and the taxpayer picks up the bill.

Amtrak says it wants to be reasonable. Lois Morasco, an Amtrak spokesperson in Philadelphia, said that only 40 of the 600 boats berthed behind the Bush River Bridge require the span to get into te bay. Futher, she said, Amtrak had offered to modify the boats so they could get under the bridge.

"It makes me furious when I amd asked how many boats need that draw span," Ritterhoff said. "It is not how many boats we have here now, it's how many we would have if they could get in and out."

"I would like to have a flying bridge," said Sullivan, "and I can't put one on becuase it won't go under the bridge when it is closed."

The obvious solutions to both Amtrak's and the yacht club's problems are not as easy as they seem. Moving the yacht clubs to the bay side of the bridge would mean dislodging the United States Army from part of the Aberdeen proving Grounds, a difficult proposition. The Army owns most of the shoreline on both sides of the river.

Building a new bridge that would be high enough for flying bridges and bigger yachts could be done, but expensively. Gregory Raugan, who worries about such things for the Federal Railroad Administration (FRA) said that no estimates have been made on a new higher bridge over the Bush, but that experience with bridges of similar length and width would put the price very roughly at between $20 million and $30 million.

The cost of repairing the existing bridge and bringin g its tracks up to 120 m.p.h. standards is estimated at $2.4 million by the FRA.

The clearance under the closed draw span, depending on the tide, is 12 feet, according to the Coast Guard; 11 feet, according to Sullivan, and 14 feet, according to Amtrak.

Amtrak has about $2 billion in mostly federal money to rebuild Northeast Corridor tracks, including the Bush River Bridge. According to Amtrak's Lawson, there are 350 bridges between Washington and Boston that need some kind of repair, and 35 that must be replaced. There is only so much money.

The Coast Guard has the responsibility of deciding the issue - at least for the moment. It has notified Amtrak of significant citizen opposition to the permanent closing of the draw span and has asked if Amtrak would like to reconsider.

"I'm sure Amtrak will still want to close the span," said Coast Guard Capt. Victor Robillard. "After they do that, we'll schedule public hearings and then try to determine te most appropriate course of action . . ."

Once before, in 1972, the Coast Guard recommended that the draw span remain. But the Coast Guard, like the FRA, is part of the U.S. Department of Transportation. In 1972, Transportation Secretary John Volpe sided with the railroad.

If this issue gets to the Secretary of Transportation again, which Robillard fully expects, Brock Adams would make the decision. Adams, when he was in Congress, fought and won the fight for substantial upgrading of railroads in the Northeast Corridor.

Leo Sullivan is prepared to continue the fight. He writes letters to Congrss and to his state legislative delegation and calls on the Hartford County Council and executive.

"The original railroad bridge across the Bush was built in 1835," Sullivan said. "It was burned down by the Confederates. I wish they'd come up here again." CAPTION: Picture 1, The controversial Bush River Bridge presents this view to members at the Bush River Yacht Club, some of whose members have boats - or hope to acquire them - that necessitates the raising of a bridge span for passage to the Chesapeake Bay. Photos by Bob Burchette - The Washington Post; Picture 2, Boats with flying bridges like this one can't make it under unraised bridge.; Picture 3, According to the Coast Guard, clearance between bridge and water is 12 feet.; Picture 4. LEO SULLIVAN; Picture 5, The Bush River drawbridge span raises for a yacht to pass through. The span is raised four times every summer weekend at a cost of $4,000. (AP); Map, no caption