Half of the Vietnam Veterans Memorial -- one of Washington's most-visited landmarks -- is covered by protective cloth and plywood, and one part or another of the memorial will be off-limits to visitors through October.

Alternating halves of the Wall will be closed as workers install a lighting system designed to illuminate the glossy black panels with museum-quality light. The eastern half of the memorial closed last month and will remain inaccessible until mid-August, when it will reopen and the western half will close.

Behind the wooden walls that keep visitors out, workers have been excavating paving stones -- about 700 pounds each -- that line the walkway in front of the Wall to dig out the buried lighting fixtures that were installed 19 years ago. While the stones are out, workers plan to restore the original grading of the walkway, which has shifted slightly, and then they'll repair the cobblestone paving, which has become slightly irregular.

Lighting has been a problem at the Wall for several years. The original system had begun showing signs of wear and became a hassle to maintain, said Jan C. Scruggs, president of the Vietnam Veterans Memorial Fund, which raised $1 million in private funds for the repair. For almost five years, the National Park Service and the fund have contracted with a lighting company to maintain the system on a weekly basis, regularly replacing gaskets and burned-out bulbs.

"Everything is just wearing out," Scruggs said.

Aside from the irregularities of old age, Scruggs said, the lights -- even when functioning properly -- left much to be desired. Names on some parts of the Wall were left in shadow, indiscernible to visitors.

The original lights are all an equal distance from the Wall, although the panels vary in height, said J.C. Cummings, architect of record for the memorial, which was designed by Maya Lin. And because the original lights are difficult to customize, the lighting was unevenly distributed.

The lights in the new system are much easier to direct and easier to repair, Cummings said. If workers need to get to the lights, digging won't be required -- removing six screws will allow access, he said. And officials expect fewer repairs with the new system. To ensure that fixtures could withstand the elements, each was tested by being immersed in a bucket of water for 30 days.

"It will be a very white light, evenly distributed on the Wall," Scruggs said. "We think the visits in the evening will improve exponentially."

In the meantime, the partial closure has left many visitors disappointed. Scruggs and others at the fund say they have been fielding many calls from tourists who had planned to see loved ones' names on the Wall, only to find that they couldn't. Some criticize the fund and the Park Service for scheduling the project in midsummer, a time for many of the Wall's 3.5 million annual visits.

"All we can do is apologize," Scruggs said. "There's never a good time for this."

The memorial is the site of two heavily attended ceremonies each year -- on Memorial Day in May and on Veterans Day in November. The June-to-October window kept the memorial open during those celebrations, Scruggs said, and allowed workers favorable weather to complete the project as quickly as possible.

The memorial was not intended to be lighted, Cummings said. But soon after the dedication in November 1982, night tours, led by lantern-carrying guides, became popular. The lights were installed nearly three years after the opening to accommodate those who wanted to visit at night.

During the excavation, workers have found many items that have fallen through cracks in the pavement over the years and become embedded in the dirt under the stones. Items collected include dog tags, commemorative coins, photographs and other mementos. The items will be stored in a Maryland facility that archives materials left at the Wall.