George Washington looks down from the heavens, flanked by Liberty and Victory in Constantino Brumidi's fresco at the center of the U.S. Capitol Rotunda.

The faint hum of a compressor sounds and a slight, almost imperceptible tremor shudders above him.

It is the dead of night, yet over Washington's head, in the space between the inner dome of the Rotunda and the outer dome of the Capitol, a team of experts labors to restore a part of a national landmark that few ever see.

Work began in June on the $44 million nearly five-year restoration overseen by the Office of the Architect of the Capitol. In Phase I, expected to finish in April 2000, workers are removing lead-based paint. Phase II, a three-year undertaking, will focus on making needed repairs, repainting the exterior and making cosmetic changes inside.

"It's the strangest set of monkey bars you ever saw. You have to be part ironworker, part kid, and part inspector all rolled into one," said Richard Kadlubowski, senior architect for Hoffmann Architects, which is supervising the first phase.

Efforts to restore the dome began in 1990 after a severe rainstorm sent nearly 25 gallons of water cascading to the Rotunda floor. Quick fixes were made, but Hoffmann architects realized longer-term remedies would be needed to preserve and protect the dome.

The firm's structural review in 1991, found the dome to be in "exceptional" shape. "As far as holding up well, I wish I looked as good at 140," said Kadlubowski. "Many of the defects we are finding were original," he said, arising when the dome was built. More than 650 non-structural defects, such as hairline fractures, have been identified so far. A key element to the rehabilitation is accurately cataloging these flaws.

But to find defects, paint must be stripped -- paint that in some areas has been in place for 140 years; paint that in some areas is 21 layers thick. Studying the cross-section of a paint chip "reads just like a streambed," according to Greg Ciotti, project manager for the construction side of Phase I. "These layers of paint tell the history of the dome," he said. A history that, apparently, is hard to scrape off.

Workers use impact tools to roughen paint layers and "blasters" that shoot abrasive sponge particles at the paint. The space between the inner and outer domes has been divided into sections for the restoration, with each section stripped of paint, cleaned and inspected for faults, a process so tedious that Ciotti likens it to "cleaning the Capitol steps with a toothbrush."

Imagine the task: Two inspectors scanning 200,000 square feet of ironwork, searching for anything unusual: A missing bolt, signs of corrosion. "We are covering every inch," Kadlubowski says. "It's a big responsibility. You are straining to make sure you don't miss anything."

Finding a defect is half the battle; documenting it is nearly as important. Each imperfection is meticulously recorded in the official defect survey book. It looks like a simple three-ring binder, but holds pages of information that will help monitor the dome's health. Each flaw is numbered and described, accompanied by a digital photograph. Inspectors also make repair recommendations. Some defects need to be "stitched" with interlocking pieces of iron; some need welding; some are too small to be bothered with. But none go undocumented.

Ciotti estimates nearly half of the first phase is completed. It isn't glamorous work. It isn't even fun work. But after a 12-hour shift, headed for the decontamination shower with protective suits caked in dust, flash rust and a fine layer of lead, Ciotto's team would tell you it's important work.

RESTORATION PLAN

Work is likely to take just under five years.

PHASE I

Objective: Remove the lead-based paint from surfaces between the dome's inner and outer shells; inspect for defects; repaint.

Duration: Began June 9, 1999, expected to end in April 2000.

Expected cost: $7 million.

PHASE II

Objectives: Repaint the dome's exterior; repair and enhance lighting inside the rotunda.

Duration: Expected to last three years. Start date slated for summer 2000.

Expected cost: $37 million.

HOW THE WORK IN PHASE I IS CARRIED OUT

The dome has been sectioned into quarters using heavy plastic sheeting and foam boards to create a contained area in which to work. Paint is removed by a blaster or other appropriate tool. Afterward, the work area is thoroughly cleaned; debris, paint chips and dust are vacuumed and all surfaces are wiped down. A team of experts meticulously inspects the ironwork for defects and records them. After the inspection, a primer and first coat of paint are applied. Work progresses virtually around the clock. At any given time, 10 to 12 experts may be at work in the confined areas.

LEAD ABATEMENT

Nearly 88 tons of lead are expected to be removed from the dome's old paint. This lead will be extracted and recycled into car batteries.

REMOVING PAINT

Removing multiple layers of paint -- some 140 years old -- is no small undertaking. In some areas as many as 21 layers of paint must be stripped away. The work is slow and uncomfortable, requiring protective gear and special tools.

PROTECTIVE GEAR

Workers take 20 to 30 minutes at the start of a shift to don protective gear. A Tyvek jumpsuit, gloves, taped at the wrists, and a face mask are essential. For work in confined spaces such as the Tholos, oxygen masks are necessary. Ending a shift takes from 40 minutes to an hour, as workers carefully remove their garb and take a decontamination shower.

TOOLS OF THE TRADE

Impact tools, such as the needle gun, come with vacuum attachments that collect most, but not all, of the debris and paint chips. These tools can be used only in areas where the vibrations will not be harmful to the artwork. Hand tools are used in areas near the Apotheosis. Paint-stripping chemicals sometimes are applied in stubborn areas.

Peener: Roughs a painted surface with a row of randomly-placed metal bits.

Needle gun: Strikes a painted area with a collection of thin nails surrounded by a bristled head to loosen paint.

Blaster: Shoots sponge particles impregnated with aluminum oxide directly onto a painted surface with a force of 90 pounds of pressure per inch to "blast" the paint off.

PROTECTING THE INNER DOME

A custom -- designed safety netting has been installed in the upper reaches of the dome. It was feared that vibrations from the interstitial work could cause paint on the inner dome to chip, dust to fall or -- worse -- a piece of the decorative cornice to come loose. The 12,000-pound safety netting is held in place by a support ring suspended from 12 outriggers. The system, made of four protective layers, collects debris and allows the Rotunda to remain open to visitors.

Visual barrier: Opaque, fire-retardant nylon

Structural netting: Capable of sustaining a 500-pound weight dropped from a height of 50 feet

Smaller netting: Designed to catch small debris such as a stray bolt or paint chips

Dust barrier

Noise levels: The noisiest tasks -- those involving impact tools -- usually are done at night. During the day, noise attributed to the restoration (measuring around 62 decibels from the Rotunda floor) can't be heard above the noise made by tourists 180 feet below (normally 75 decibels).

Condition of the dome:

The health of the dome is exceptional. A structural review of the dome's 8.9 million pounds of ironwork in 1991 yielded about 650 non-structural defects, such as hairline fractures or patches of low-level corrosion. Many defects appear to have occurred as a result of the iron's natural heating expansion and cooling contraction.

The Capitol's original dome, completed in 1824, was made of wood covered by copper. By 1850, it was considered too small for the expanding Capitol and feared to be a fire hazard. In 1856, it was removed. The new dome -- made of cast iron -- was based on the design of the Pantheon in Paris and featured inner and outer shells that form a double dome. The entire assembly rests on 36 supporting trusses attached to the Capitol's original foundation. The exterior was completed in 1863 and the interior in 1866.

Cast iron: Engineers determined cast iron to be the cheapest and most lightweight material with which to build. The new dome weighs only 19 percent more than its predecessor, despite its larger size.

Cost of today's dome:

When built: $1 million; $10.6 in 1999 dollars

Cost of Phase I restoration: $7 million

Estimated cost of Phase II restoration: $37 million