THE EIGHTH ANNUAL Marine Corps Marathon will lure twelve thousand-plus running enthusiasts to the Iwo Jima Memorial grounds this Sunday at 9 a.m. -- and probably as many spectators, many of whom hope to capture pictures of friends as they breeze (or wheeze) along.

With a little ambition, planning and legwork (or, better yet, a bicycle), you can take things one step further: There's no better subject for a photo essay than a marathon.

The photographic action starts well before the race, as runners arrive, check bags and begin stretching in improbable and occasionally amusing postures. Marathons usually boast plenty of offbeat T-shirts, wild costumes, clever signs and pageantry.

Just before the start is the time to catch tight shots of runners' faces, as they await the firing of the 105mm howitzer that starts the 26- mile journey. Or clamber up the hillside surrounding Virginia Route 110 and photograph the whole pack in its early surge.

Even better, head down to George Marshall Drive, a few hundred yards south; the runners pass below on Route 110 just after the start.

Shooting a long-distance running event is a good way to learn the rudiments of "stop-action" photography, since most marathoners move more slowly than competitors in other sports. To "freeze" a runner heading straight at you, you can use a shutter speed as low as 1/125 second. If the same runner is moving at right angles to you, you'll need a faster shutter speed.

How fast? That depends on whether you want to stop all motion, or just some of it. Different parts of a runner's body are moving at different speeds: Trunks and hips are nearly still; upper parts of legs and arms are somewhat faster; and feet and forearms are quickest of all. At 1/2000 or 1/1000 second, a runner shot in profile will be tack-sharp; at 1/250 or 1/500 second, feet and forearms will blur.

It won't be easy to pick your friends out of the pack early in the race -- runners are too closely bunched. Once they head into Georgetown, however, they begin to spread out. M Street is a festive spot with lots of sign-wielding fans. Some wide-angle shots of runners and the pub-lined streets will capture the flair of the moment.

For scenic beauty, the best spot is a few miles farther, along Rock Creek Parkway between Pennsylvania and Independence avenues. Here, fall foliage provides a colorful backdrop for the runners and the path is less populated with spectators, affording you more photographic elbow room.

Even so, get there well before your running friends do, to stake out a spot. If you wait for a runner to pass by before you focus, frame and snap, you may be too late. Instead, pick out an imaginary line up the road; include a reference point such as a roadside shrub or crack in the pavement. Set an appropriate shutter speed, preview depth of field, then focus on the landmark. As your runner of choice strides across the imaginary line, snap the picture.

A tripod is a great help, if you have one. Not only will it ensure that you don't move your camera position (and your area of sharp focus), but it will also enable you to peer into the distance for your subject and follow him until he approaches your imaginary line. Then you can return to your tripod and make the picture.

Once you've made a few "stop-action" photos, try more exotic shooting. Panning is great for conveying a sense of motion and is particularly effective with colorful, but distracting, backgrounds. Stand at right angles to the runners' line of travel, and pre-focus on the path they'll take. Set your shutter speed somewhere in the 1/15- range and adjust your aperture. Then turn your upper body about 45 degrees toward the approaching runner. As or she enters the viewfinder, turn frontwards to keep the subject in the viewfinder's center as he or she passes. Press the shutter at the instant you're facing front again, but continue turning 45 degrees to the right.

Like a good golf swing, proper panning depends on rhythmic motion and a good follow-through; if you stop as you press the shutter you're bound to jerk the camera. Correctly done, a panned photo will show blurred arms and legs, but a sharp face and trunk; the background will appear as a series of parallel, horizontal streaks.

For an interesting variation, hook up an electronic flash with its power control set for one stop less than the existing light reading indicates. (If your meter reading is 1/15 second at f8, set your strobe at f5.6; leave your shutter at 1/15 second.) Then pan as described above. The result should be a central tack-sharp flash- frozen image, surrounded by a pan- like blur.

As you shoot the race, avoid monotony by varying your shooting angle and lens focal length. Telephoto lenses will compress the image area of a photo from front to back, making the distance between runners appear less than it really is. That makes teles useful for exaggerating the startling sight of a road- wide pack of marathoners barreling toward you. A tele's short depth of field at wide apertures can be used to render one runner in sharp focus while blurring those ahead and behind, thus adding to your picture's impact.

Tele and wide-angle lenses create different emotional effects. A tele shot of a lone runner trotting down the street will make buildings loom ominously behind him, emphasizing the aloneness and self-absorption of many athletes. A wide-angle shot of the same scene will give a sense of spaciousness and the flow of energy from crowd to runner.

Shooting from curb level with a wide angle as spectators reach out and cheer a passing runner or as water-stop attendants reach out with refreshment will pay off in dramatic pictures.

If you can pull it off, make it back to the Iwo Jima memorial for the finish, homing in on runners' faces as they climb the steep hill to the memorial, and capturing their exhilaration as they finish. You'll have put in a pretty exhausting effort yourself, by that time -- but you'll have pictures worthy of your workout.