The National Park Service says a scratch noticed by a park ranger on the Vietnam Memorial last weekend is a flaw in the stone work and has been there since the memorial was erected six years ago.

Officials at first said the vertical scratch was the result of vandalism, which would have been the second defacing of the black granite wall in two months.But on Tuesday park service spokeswoman Sandra Alley said:

"We're confident it has been on the memorial since 1982. We're both relieved and embarrassed."

Park service authorities initially concluded after Ranger James Lance reported the 4-inch-long mark on Sunday that it was the work of vandals. They said the wall with its 58,156 names of Vietnam War dead is so hard that the scratch had to be deliberate.

Lance, who has been assigned to the wall since October, said he first noticed the scratch Sunday morning.

"It's one of those things. You walk by 20 times and never see it and then one time it hits you between the eyes," he said.

The memorial is the most popular in Washington and attracts 12,000 to 15,000 visitors a day.

Authorities said complaints poured in Monday after news reports of what they had thought was vandalism.