THANKS TO SOME enterprising Washingtonians, there's a place in town where youngsters can see the inner workings of fire-alarm boxes and traffic lights, figure out how to play familiar tunes on African instruments or make their own printing stamps and braid rugs - all for free. It's called the Capital Children's Museum and it's located in several unused rooms of the Lovejoy Elementary School at 12th and D Streets SE. The museum introduces young people to the way things work by allowing them to handle artifacts, watch slide shows and other presentations and come up with their own creations of various instruments, buildings and tools.

Though it has been around for less than a year, the museum has already developed a large and enthusiastic audience. More than 35,000 people - from as far away as the Middle East and as nearby as the next block - have visited the museum; the guestbook carries the names of Mrs. Sadat and Mrs. Begin, each of whom dropped by when their husbands were in town on diplomatic trips, as well as hundreds of school children from the District. Children and parents alike are interested in the "hands on" approach, one not usually tolerated in the same dignified exhibit halls of Washington.

Encouraged by the response, the museum now wants to move to a larger - and less makeshift - building. They've picked an empty house in the H Street NE renewal area. Built in 1874, the rambling and somewhat run-down structure and its adjacent open space occupy an entire city block. The museum's plans call for a garden, a recreational area and parking, as well as larger exhibition areas, work rooms for youngsters and storage and office space. A number of activities are planned for neighborhood residents, young and old alike.

The museum plans to seek about $3 million from a special fund in the Department of Housing and Urban Development to pay for the site and its renovation. HUD requires that such projects have local support, and Mayor Walter Washington has already approved the plan, as have several community groups in the H Street area. The only endorsement still needed is that of the City Council, which plans to take up the matter today. We cannot think of a single reason for the council not to give this worthy project its enthusiastic support.