In the city and suburbs where wildlife disappeared with the arrival of bulldozers and lawnmowers, some carefree local residents have decided to forgo their manicured landscapes and let their back yards go natural.

For these participants in the National Wildlife Federation's back yard habitat program, there is something comforting in being surrounded by small, wild things - the birds, raccoons and squirrels they feed regularly and the pastiche of colorful flower beds.

"Part of the fun of growing things is not knowing what there will be here from one day to the next," said Alice Grant, who has converted her once denuded, half-acre yard in Columbia, Md., into an intricate blend of curving flower beds, bardwood mulch carpets and radomly growing wildflowers. A dense forest as a backdrop - the forest that was there long before the bulldozers came.

"People drive by and say look at the field of weeds," she said with a wince as she point out pine seedlings, vibrant goldenrod, wild strawberries and wispy field asters among the so-called "weeds." I'm beginning to resent those comments tremendously."

The backyard wildlife program, which was started four years ago to encourage sources of food, water, shelter and reproductive areas in urban and suburban lots, has attracted 900 participants around the nation, including 33 in the Washington area.

"Even a window box can be enough," said naturalist Craig Tufts of the wildlife federation. The agency, which is based here, supplies abundant information about how to contribute to the urban wildlife movement.

Loraine Vaa, a volunteer naturalist in McLean, joined the program because she felt a responsibility to aid homeless wildlife whose natural habitats are being destroyed by suburban development.

"When something dies I try to replant something with berries (to feed birds) and when a tree falls, we don't take it out because birds use it for nesting," she said.

"Anyone who wants a neat yard won't have much in the way of wildlife," said Vaa, whose lot sits in front of the forest.

She rarely sprays to rid the area of bugs because the dozens of birds eat the insects.

A raccoon arrives at her back door nightly for food, and a bluejay "asks" her for peanuts. The back yard chipmunks wage ferritorial wars with the front yard chipmunks and she learns much from watching how the birds' pecking order works.

She leaves a brush pile on one slope of her third-of-an-acre lot and a compost pile nearby. Rather than being devoured by an electric disposal, food scraps are saved for the wildlife. One bird bath sits on the ground for birds that don't like to bathe on a pedestal and suet laced with peanut butter and bread crumbs hang from trees in used cans during the winter."I think people are definitely more conscious of nature, especially now that so many trees are being cut down for subdivision after subdivision, but you know," she said, "some people are afraid of the outdoors."

Not the Grants in Columbia. "My mother did this kind of thing," said Mrs. Grant, as she eagerly pointed out - and talked to as personal friends - some of the 300 varieties of plants in her yard.

As a youngster, she said, "we had a big place, with a pond, sloping down to a lake. Very soon after we moved in, my mother decided to let it grow wild. When I was teen-ager, I was too dumb to appreciate it."

In later years, Mrs. Grant turned to gardening, and when she and her husband Clifton retired in Columbia from New Jersey, they saw their bare lot as a limitless challenge.

An early addition was a fish pond. Now, two years later, it is the home of 32 goldfish and 18 frogs. At the rate they are proliferating, the fish will number 1,000 in three years, Grant figures.

"We think up something new each week," Mrs. Grant noted, noddling toward a newly built platform where raccoons climb for chicken bones.

Railroad ties hauled out of the Columbia dump line a path into the woods. In hopes of attracting deer, the Grants placed a salt lick on the rear fringes of their property. "Even in the city," Mrs. Grant said, "if you put out a bird feeder, it's amazing. The birds will eventually find it."

In the midst of all this foliage lies only a small plot of closely trimmed grass, the size of a badminton court.

"We encourage landscaping without lawns," Mrs. Grant said. "Mowers are noisy and weeding flower beds is better exercise anyway."