The first thing to know about the Pentagon Memorial design unveiled yesterday is that it is in exactly the right place -- only 60 yards or so away from the point of impact and directly along the flight path taken by the murderous plane that struck the building on Sept. 11, 2001.

The second thing to say is that the competition-winning design by two young New York architects does much to honor and intensify the meaning of this already significant location.

Conceived by Julie Beckman, 30, and Keith Kaseman, 31, a pair of architects not many years out of graduate architecture school at Columbia University, the design ingeniously links the site with the terrible event that took place there on a particular day.

It manages this trick without fanfare and without any of the symbolic devices we customarily associate with memorials. There are no representational images, military insignia or explanatory texts. But visitors are sure to get the message almost immediately, and to keep getting it throughout their stay, for the design promises to have a cumulative impact.

Called "Light Benches," the design is composed of 184 16-foot-long benches, arranged in parallel rows under clusters of maple trees on the nearly two-acre site. Both the organization and number of the benches ties the memorial to that specific day -- the rows are angled toward the Pentagon's west facade precisely on the path taken by the attackers, and 184, of course, is the number of deceased victims.

This identification of site and event is further intensified by linking each bench with an individual victim, whose name is to be incised on the narrow end face of a bench. The chronology of the rows -- they are to be sequenced by year of birth -- adds another level of pathos. In traveling the distance from youngest to oldest -- from 3 to 71 -- visitors will comprehend something important about that day.

Probably the most unusual aspect of the design is the shape of the benches, which the designers refer to as "memorial units." Rather than the conventional long seat with supports at two ends, these resemble diving boards, with a rigid cantilevered seat extending about six feet from a heavy base. Underneath the cantilevered seat of each bench will be a narrow pool of water.

Because the open-ended form gives a sense of directionality to these benches, the shape allows the designers to add another layer of information about the event. Benches identified with occupants of the plane will face in one direction, and those representing people in the Pentagon at the time of the attack will face another direction.

Terry Riley, chief curator of architecture and design at the Museum of Modern Art and chairman of the 11-person memorial jury, yesterday noted the correspondence between this design and the orderly rows of grave markers at Arlington National Cemetery. Yet the fact that benches replace grave markers in this design, and that visitors are invited to sit on them, will give an eerie intimacy to this encounter between the living and the dead.

The fact that these are to be "light benches," illuminated with halogen lamps built into the structure, promises to lend a touch of magic to the solemnity of the place, particularly at night.

Light will be important during the daytime, too, say the designers. Both sunlight and artificial light will create subtle reflections on the narrow pools of water and the polished aluminum undersides of the bench seats. The dappling effect of sun coming through the leafy trees will add to the subtle, changing pattern, they say.

There is no question that the trees are phenomenally important to the overall effect. A real danger of the design is that the unconventional benches, as physical objects, will call too much attention to themselves. Trees are thus essential to help soften the relentless linearity of the benches. Let's hope that there are enough trees (and that they're of sufficient maturity right from the beginning) to do the job.

Precise workmanship and quality materials in the benches themselves are essential, too. If they come off looking capricious and odd, rather than inevitable and beautiful, the overall design will suffer immeasurably.

Both benches and trees will stand upon a paved surface made of stabilized gravel. The material, says Beckman, "will be hard enough to roll a wheelchair or a stroller on, and soft and crunchy enough to hear your own footsteps."

Public access to the memorial will be via a pathway from the Pentagon's south parking lot and nearby Metro station, or from public parking lots in Pentagon City. The memorial, in other words, won't be that easy to get to -- but in all likelihood it will reward the effort. Beckman and Kaseman came through with a thoughtful, consistent design for an open, contemplative space with an emotional edge.

Of course, we'll have to wait and see how their ideas translate to reality -- but the wait won't be long. Pentagon planners seem confident that the memorial will be ready by Sept. 11, 2004.

A contemplative space with an emotional edge: 184 illuminated benches will commemorate the victims.An artist's rendering of the memorial at night shows the effect of the halogen lamps built into the "light benches."