CITY HALL'S keepers of the public space are taking seriously the song, "This Land is Your Land": they're inviting community groups and individuals to join in the care and weeding of hundreds of little parks and tracts around town--and they're getting a lively response. The whole idea, patterned somewhat after the beautification projects for the bicentennial, is simple enough: give people a square inch and they'll take a square mile or two and maybe more if it's in their neighborhood.

Naturally, it's being sold as a dandy way for citizens and government to join hands for the greater municipal good--but, in fact, good old-fashioned neighborhood and organizational pride is turning out to be the real spark. Either way, D.C. Transportation Department director Thomas M. Downs has taken a personal interest in this project and already has enlisted a number of participants. The Capitol Hill Hospital, for example, has agreed to beautify a park across the street at Massachusetts Avenue, Constitution Avenue and 8th Street NE; and the Lustre Cleaner and the 7-Eleven in the 3200 block of Pennsylvania Avenue SE have agreed to maintain a tract in front of their stores. Even some federal government employees are going local--a group of Department of Education workers has taken over land across from its office.

Businesses may also participate by contributing to a fund that will be used to provide awards and buy additional materials for the parks. A group "adopting" land is asked to agree to do a serious and ongoing job, but the transportation department will help with advice on planting and pruning, landscaping and flowers and vegetables; and officials will visit each area once a month to award "points" to competing groups.

Given the bumper crop of broken glass, weeds and trash that has yet to be harvested, the city government could use a little help from its friends. There are about 100 businesses and organizations next to or near 25 of the 287 parcels that have been put up for grabs. They, as well as anyone else, may learn more about the various projects from the city's staff at 727-5691 or 727-9639. If the response continues as it has, by spring the city should be full of eye-catching growings-on.