Shortly after 1 a.m. yesterday, two-dozen Metro construction workers began moving a massive 148-foot-long steel garden from the shadows in the middle of the Capitol Beltway toward the overpass 400 yards away at Pooks Hills.

A team of eight ironworkers marched along-side the trough-shaped steel beam, weighing 47 tons or the equivalent of 24 automobiles, as it was pushed and pulled on dollys by tracks along the blocked off Westbound lanes of the highway.

Awaiting the hard-halted entourage and the steel girder was a giant crane that, during a two-hour ballet with the ironworkers in the gloom and chill of the morning, would hoist the beam and another like it to connect another section of the Metrorail bridge over Interstate 495.

It was a dance against time, forced by the need to close the Beltway for the dangerous task. It had to be completed in the five hours between midnight and 5 a.m., a time when the light but steady Beltway traffic could safely be rerouted for a mile through the residential fringes of Montgomery County.

For Bob McDonald, ironworker superitendent, his crew and the Expressway Constructors supervisors - all of whom are accustomed to working day shifts - it was "cold, damp scary." In near darkness aid by a dozen small spotlights, they gingerly, manipulated steel cranes and girders nearly a half a football field in length and cables so heavy, knowing that any slight mishandling could result in a broken leg or a severed finger.

"We can't see everything, that's going on," McDonald explained yesterday.

Nevertheless, to these men the job was "just routine", another bridge for the ironworkers whose 18-inch-lug wrenches - a trademark of sorts - clanged in the night against their belts.

There was of course, the pressure of finishing the job on time, a 5 a.m. deadline not met last Thursday when a similar operation at the same spot at 7.55 a.m. after nine miles of rush hour traffic had backed up eastward.

By 1:30 a.m., the crane's cables were fastened to the loops of steel welded to the girder, and crane operator Jack Karpiak began the hoist.

"There's not too much to it," apprentice Doug Schroeder said of 32-year-old Karpiak's job. "It takes a little coordination."

Within minutes the girder had been lifted by the cranes 100-foot-long aerial boom to the point where it was even with the brace into which it would eventually come to rest 31 feet above the highway. A series of reverberating clangs filled the air between the surrounding concrete overpasses as the girder and brace met.

"Tagline coming down," an ironworker shouted as the cables fell. Ironworker Roger Sweeney stood 40 feet up on the frame holding the girder and signalled, first with his left arm, then his left leg, to foreman Pete Walker below, indicating how the crane should shift the girder for proper positioning.

Sweeney momentarily disappeared while McDonald grimaced and complained about the danger of working steel in the dark. "He could have gotten his toe pinched up there," McDonald said.

Meanwhile, the ironworker at the other end yelled that his connection was "fouled" and Karpiak began gentle crane movements to jockey the girders into place.

Sweeney's crew, the "raising gang," ended their duties and another crew, the "bolting up gang" began their aerial walks across the girder. As sparks showered to the highway below, the bolters burned off the lifting hooks with acetylene torches.

Mike Aldrich, an inspector for Bechtel Corp. paced the work site quietly. "I don't mind this," he said of the overtime duty, "but I wouldn't like a steady, diet of it."

Aldrich, an engineering student at the University of Maryland, missed an exam because of the extra duty. "I'missed one last week, too," he said.

As the second girder was positioned, along penetrating shriek rent the misty night air, the sound of massive metal girders grating one against the other. Sweeney had less guiding to do this time. By 3 a.m. the girder was in place.

"See, I wasn't so dumb after all. I knew we would be done early," laughed Aldrich, who had packed a sleeping bag in his car for the anticipated nap between the night shift and the 7 a.m. day duty.

Meanwhile, Andy Neyman, project manager for Expressway Constructors, was getting tired. His men's safety was on his mind as he supervised the operation.

"It's easy to "rip out here," he said wearily. "Everything is heavy. Everything weighs hundreds of pounds and you have to exercise extreme caution. It's hard to see. A lot of people have lost their fingers just by small things in working with steel. And the mud. The rain didn't help us any."

Later Neyman called off plans to continue work at the same time Wednesday and Thursday morning because of incomplete preparations. Early next week the crew will be out again in the dark, hoisting even larger 200-ton girders to finish the job.