FIVE-YEAR-OLD Christopher took my hand and whispered, "This is great, Mom."

Here we were on an evening hike looking for beavers in Rock Creek Park. We could see no traces of beavers, the creek looked murky and trash-strewn, absolutely nothing noteworthy had happened, but Christopher still thought it was great. Chalk one up for the kid.

Our walk that evening didn't bag us a beaver sighting, but the beauty of beaver hikes doesn't lie entirely in seeing these toothy rodents in the wild. That's part of the thrill, to be sure, but there's also the pleasure of being outdoors in the early evening, before the fireflies start their nocturnal flickering. There's the fun of walking quietly along a creek, whispering to each other, all senses on alert for beaver dams or dens.

While most kids don't need a good reason to take a walk in the woods, having a goal adds a treasure-hunt element to hiking. Beaver hikes, as opposed to generic, no-name hikes, have a real, simple goal: Spot a beaver in its natural environment. Runner-up rewards in beaver hiking include finding a beaver dam, identifying lodges or dens and locating small tree stumps chewed to pencil-tip formations by a beaver's chisel-like teeth.

A successful beaver hike almost always starts by picking the brain of a knowledgeable park ranger. These are the folks who know the terrain of their respective parks; if there are beavers to be sighted, the rangers know where to look. They can identify which lodges are active and will often offer hints on identifying landmarks that tell beaver hikers whether they are on the right trail.

Beyond pinpointing a likely spot, beaver hikers will do well to remember that beavers are primarily nocturnal animals. They rarely stir during the heat of the day, preferring to sleep and groom themselves in their lodges. The National Zoo even has a closed-circuit TV in the lodge of the beaver couple residing there, so that visitors can see them despite their inactivity during the busiest zoo hours.

Hiking in the twilight is the best time to spot a beaver in the wild, although we recently enjoyed a daytime beaver hike in Prince William Forest Park. On that walk, Christopher and I found a whole field of gnawed-down saplings, located an impressive beaver dam and were rewarded with a game of hide-and-seek with a white-tailed deer rather than a beaver.

Other suggestions for beaver hikers include taking binoculars (just in case you can't find a good way to get close to the water's edge) and being as quiet as possible when approaching the possible beaver site. And when you find a live one, savor your small intrusion into its life, because, in most cases, the moment won't last long.

Our first beaver foray took us to Piscataway Park near the National Colonial Farm in Accokeek, Md., where ranger Greg Kneipp had directed us to the park's Accokeek Creek Site. It was a misty, Friday evening with a drizzle falling from the gray skies. We got slightly twisted on the directions and ventured further out than necessary on the park's boardwalk through the marshes. Out in the middle of the swampy terrain, a large beaver lodge rose among the pickerel weed and cattails. We couldn't get close to that lodge for observation, but we watched a few herons standing guard on the shoreline of the Potomac.

We then headed back to find the dirt path that the ranger had told us about. My 9-year-old daughter Laura and her friend Lily Raff, 10, were pleased with themselves for locating the path first and led the rest of us off to find the dam and lodge. We walked quietly, the children shushing each other, and then, there he was. A big, fat beaver glided slowly through the water, seemingly out for a recreational spin around the marsh. His ears and nose poked above the waterline while his wide, furry body was visible right below the surface.

The kids froze in awe and excitement. We watched for almost five minutes and then I ruined it by whispering, "Pass the binoculars."

That did it. The beaver became stiff with alertness; he lifted his big flat tail and smacked the water's surface with a resounding warning to his fellow beavers. Diving down to safety, he disappeared.

That's about as good as it gets for beaver hikers. EAGER BEAVERS

Some parks offer ranger-led beaver hikes. To find out about these, get on the mailing list for Kiosk, the National Park Service publication. Send a card with your address to Toni Carroll, Room 106, Office of Public Affairs, National Park Service, National Capital Region, 1100 Ohio Dr. SW, Washington, DC 20242.

Besides exhibiting two bashful beavers, the National Zoo also demonstrates the complexity of beaver engineering with its exhibit on beaver lodge construction. The Baltimore Zoo, in its terrific children's area, has an underwater, concrete and glass beaver lodge that children can enter to experience the habitat from a beaver's perspective.

Check with the naturalists and rangers in the parks or nature centers closest to your home to find out about nearby beavers. Before setting out on any hike, it's a good idea to pick up a map from the park's visitors center. Here are a few suggestions from various rangers:

C&O CANAL --

Ranger Chris Lee suggests several beaver-spotting possibilities, including the area between Locks 15 and 16 near the Great Falls Tavern Visitor Center. There are also beavers on the southern end of the Billy Goat Trail, about one-half mile from the trail's southern marker near Old Angler's Inn -- directly above where hikers cross a stream by jumping from rock to rock. Call 299-2026.

PISCATAWAY PARK --

Take the Beltway to Exit 3A, Indian Head Highway South. Turn right at Livingston Road, then right at Bryan Point Road. The park is four miles down on the right. At the Accokeek, Md., Creek Site, one lodge is easily seen in the distance from the start of the boardwalk leading over the marsh. For a close-up view of a dam and a lodge built into the dam's corner, turn right on a dirt path before the boardwalk; both are easily seen from a wooden viewing platform on this small trail. Call 763-4600.

PRINCE WILLIAM FOREST PARK --

Take I-95 to Route 619 West. Go 1/4-mile to park entrance on right. From Parking Lot H, take Trail 10 towards the center of the park; traces of beaver activity are easily found where the trail intersects with a small creek -- a 15-minute hike from the parking lot. Beavers also reside in Quantico Creek, found on a longer hike along the Farms to Forest Trail near the Oak Ridge Camp Ground. Maps of the park are given at the entrance gate when paying the $3 park user fee. Call 703/221-7181.

ROCK CREEK PARK --

A ranger at the park's nature center told me that two families of beavers have lived in the park since 1983. We couldn't find them, but more observant beaver hikers may. Look in two spots: directly north of Pierce Mill or near picnic grove No. 8 where Rock Creek and its tributary, Pinehurst Branch, intersect. Call 426-6829.

Mary Ellen Koenig last wrote for Weekend about area herb gardens.