T HE VIETNAM VETERANS MEMORIAL

turns five this week, and, to the casual observer, it hasn't changed all that much. The polished black granite walls are still the same; the impact of the names is still harrowing. But to keener eyes, like those of photographers Sal Lopes and Wendy Watriss, who have produced two of the largest documentary records of the Wall, it has definitely gone through some changes.

Lopes, 44, went to the dedication ceremonies in 1982 and has since made some 30 trips to the monument from his home in Boston. "I went to the memorial for the same reasons a lot of other people went there," he says, referring to four friends whose names are among the 58,156 on the Wall. Along the way he's become part of a family that has grown up around the memorial. "We each seem to be making a pilgrimage there," he says.

Lopes' most dramatic moment at the memorial didn't even yield a photograph. In 1983, as he was about to photograph a veteran, the man tried to slash his wrists. Lopes dropped his camera and stopped the man in time.

That incident helped Lopes win the confidence of the core group of veterans who regularly congregate at the Wall. "They learned that I knew where to draw the line," he says, "that I would put my camera down. In the long run, I got much more access."

Over the years, Lopes has seen an increase in POW/MIA demonstrators turning "violent and scary" in confrontations with the police. He has also observed an increase of what he calls "tree vets," veterans who linger on the perimeter, still unable to face the emotional force of the Wall.

Watriss, also 44, comes to the memorial from another direction -- literally and figuratively. She travels up from Houston and usually shoots in black and white while Lopes uses color. She didn't know any of the names on the Wall personally but started photographing the memorial after years of documenting the Agent Orange issue. The Wall, she says, "is one of the few places in the United States where I see the public collectively coming to terms with our Vietnam policy."

She thinks the mood at the memorial has been evolving from gung ho to hell no. "Now there is a lot less evidence of the America-first super-patriotism of the early Reagan years," she says. "There are more teen-agers, more peace paraphernalia being worn. More questioning about what it all means and how it relates to what is happening in the United States and Central America today."

Unlike Lopes, Watriss feels that the POW/MIA groups have actually quieted down. "For a while there were groups that almost seemed to take possession of the physical territory," she says. "I think the veterans have recaptured some of their psychological space at the memorial."

Both photographers speak of cutting back, of going on to other things. Says Lopes, "There's a lot of grief I take home every time I go to the Wall." But this week will find them back in town with their cameras. "I guess I'll always revisit the memorial," says Watriss. "It brings me in touch with a part of the American psyche that I respect."