Redecking the crumbling Woodrow Wilson Bridge, a construction worker recently remarked, is a little like learning a musical scale. First you learn the notes, and then each day you play it faster and faster until it's something you can do in your sleep.

Shortly after midnight yesterday, tons of machinery and dozens of men stood on a 40-foot-wide section of the bridge's traffic-free westbound lanes and slowly began a project that, like learning a musical scale, is supposed to gain speed during its scheduled 14-month, evening-to-dawn, five-days-a-week reconstruction.

The trouble is that nothing quite like this $23.7 million job has ever been undertaken, say engineers planning the nocturnal transformation. On paper, anyway, 80 or so workers, Monday through Thursday, will close four of Wilson's six lanes to traffic from 8 p.m. to 6 a.m. (from 9:30 p.m. to 7:30 a.m. on Fridays).

Using new technology and new high-speed construction techniques, workers for the Cianbro Corp. in Pittsfield, Maine, will then rip away about 138 feet of the Wilson's 5,905 feet of potholed roadway every night and replace it with stronger, lightweight, plastic-coated concrete held in place with a quick-setting super glue. All of this without interrupting Wilson's 130,000 daily rush-hour commuters.

"This bridge is unique in that respect," says James R. Bryce, Cianbro's chief engineer on the federally funded project. "This will be the first time a major reconstruction of a bridge has been done while maintaining rush-hour traffic."

For the last few years, more and more of the concrete from the 21-year-old Wilson Bridge has fallen, bit by bit, into the Potomac River and upon the Virginia and Maryland shores that anchor the gently arching span. Hubcap-sized potholes, frequent emergency patchwork and subsequent traffic standstills became a way of life for motorists.

But a slab of precast concrete measuring 12 feet by 46 feet, weighing 27 tons and waiting on a barge 60 feet below the bridge was set to begin ending all of those headaches. More than 1,000 such slabs are being brought 90 miles by truck from Winchester, Va., to Alexandria, where they are transported by barge to the bridge.

The slabs, reinforced with steel, will be bolted down with 36,000 metal rods and cemented into place. In the past, Bryce said, the type of concrete required for such a job took nearly a month to set properly. On the Wilson, however, traffic will drive over freshly completed work every day. The slabs will be held in place by a polymer concrete that closely resembles plexiglass. It will be poured into 18 six-inch-high metal molds that will support the slabs like pedestals. In one hour, the polymer concrete will set and be ready to withstand 5,000 pounds per square inch.

To prepare the way for the slabs, workmen yesterday morning cut away chucks of the bridge's old roadway using a tractor-like buzz saw manned by a single worker. Tony Bourst sat in the side-mounted driver's seat and drove the diesel-powered saw to the edge of bridge. The cutting wheel, 7 1/2 feet in diameter, chewed at the old roadway with its 70 super-hardened teeth, its stabilizing arms extended in front like a crab's claws.

A deafening din filled the rain-sprayed air. After about an hour and a half, Bourst inched the machine away, leaving a trail of broken concrete and reinforcing steel nine inches deep. "Everything's okay," said Paul Gudelski, the state's assistant project engineer overseeing the redecking. "We just got to get use to everything."

Yesterday's cutting went slow. But in future weeks, engineers say the huge saw should be able to cut out a 40-ton hunk of concrete in 30 minutes. After the old roadway is cut, workmen move in, working on top of the bridge and under it from special decks suspended over safety netting, to rig cables around the old pieces of roadway. Cranes on the shore and on barges then lift the concrete from the bridge and lower it onto waiting barges.

Meanwhile, air compressors rumble as workmen sandblast and paint the newly exposed steel beams on which the new slabs must be fastened. Much of the Wilson's deterioration was caused by severe weather and by de-icing salt that crack concrete and rust the interior reinforcing metals inside the bridge's concrete, Bryce said. That is why both the new concrete slabs and the reinforcing bars inside them will be coated with weatherproof plastic.

When the job is completed in early 1984, Bryce said, the Wilson will not only be stronger but a few inches taller because of the pedestals supporting the roadway slabs. It will also be 14 feet wider and for the first time will allow shoulders with emergency lanes.

When the Woodrow Wilson Bridge opened Dec. 28, 1961, it was designed to handle an estimated 85,000 cars a day. By 1977, an average of more than 105,000 vehicles used it. Today, the number stands at 130,000.

"Lane for lane," said Thomas Crosby Jr., a spokesman for the American Automobile Association, "it's the busiest bridge in the country." Much too important a part of Washington's transportation system, he said, to ever be closed for extended repairs. And if plans go well, it won't have to be.

Said Bill Hoffman, the man who owns the giant buzz saw atop the Woodrow Wilson, "It's one of the most thrilling things I've ever done.