Office workers and passing commuters in Rosslyn, long accustomed to the dust and clutter of construction, are getting their first glimpses of artist Nancy Holt's handiwork these days. They may not know what to make of the odd sight: a large, gray sphere rising from the torn earth of a curious leftover corner at the southern edge of the hard Rosslyn environment.

But when the park is finished--with any luck that will be in late November--it probably will draw raves, for Holt's design is innovative, inviting and thought-provoking.

The idea of commissioning an artist to design an urban park, to control the entire spatial experience and not just to add a sculptural touch, is worth careful study on the part of politicians and planning commissions in other cities.

It is a good idea and a bold one, but should not be lightly entertained. A key to success--the key, perhaps--is selecting an artist who is up to the job. Most are not. Designing a park entails attention to functional and practical requirements that most artists, by temperament and training, are not equipped to deal with.

On the other hand, the right visual artist can bring a fresh perception and a holistic vision to the enterprise. Isamu Noguchi is such an artist. So is Holt, a New Jersey-bred New York artist who for more than a decade has been making sculpture that responds, often in strange, surprising ways, to the physical and psychological conditions of specific sites.

She was inspired by the isolation and dome-like sky of a desert in Utah, for instance, to place huge concrete conduits there, conduits with holes bored in them so that the burning sun would record the daily passage of the Earth upon their shadowy interior surfaces. In a green Dublin park she mimicked existing irrigation systems to create an airy, fanciful structure out of silvery water pipes. In Oxford, Ohio, on a sweeping lawn near ancient Indian mounds, she buried pipes in a mound-like structure that aligns itself with the magnetic North Pole.

Holt's park in Rosslyn, located in front of a new ribbon-window office building on two plots of ground where Fort Myer Drive and North Lynn Street come together, also involves measurement, with the difference that the site lines direct the eye towards specific aspects of the park itself.

The large gray sphere now in place--it can be seen from a car coming down the Arlington Boulevard hill towards Washington--is the first of five such spheres that will be placed at key locations in the park. Holes bored in the center of two of the spheres and two see-through tunnels buried in the undulating earth will focus attention upon the relationships between these forms. (Holt, characteristically, refers to these relationships in celestial terms. "There will be eclipses," she says.)

Another of Holt's strategies is a sort of studied contrast between natural and man-made forms, and between hard and soft materials. She chose a Gunite surface for the spheres, she says, because concrete was the "natural material" for Rosslyn, but the lightly textured surfaces have a lunar-like quality that should give the park an intense, almost apparitional appearance. At the same time, Holt provided the right practical elements, places to sit and eat and schmooze, so that the park will be a commodious, as well as a contemplative, place to visit

Gunite is a dry mixture of Portland cement and sand that is driven by air pressure through a tube and moistened at the nozzle end as it is sprayed on. For Holt's purposes it was the ideal material--extremely durable and yet flexible--but finding someone to make the spheres was a big question mark.

"We'd never been asked to do anything like it," says Mark Wilkinson of Paddock Pools in Arlington. "When Nancy walked through the door, the fun started." Wilkinson contrived an ingenious method of spraying the Gunite over Styrofoam molds reinforced with steel rods and chicken wire, and he invented an odd-looking, but effective, circular screed to smooth the uneven surfaces after spraying.

Holt has received impressive technical and bureaucratic support throughout the project, she says. This is another key element in its success. The unusual contract was signed in 1979, after the Arlington County government had received an $18,000 matching grant from the National Endowment for the Arts.

Its final cost will be in the neighborhood of $200,000, according to Thomas Parker of the county's economic development division. Parker was an early and enthusiastic supporter of Holt's ideas, and helped to nudge the project along whenever it ran into financial or organizational difficulties.

Holt's is not the only new park in Rosslyn. "Annie's Park," a tiny vest pocket affair between North Moore and North Lynn streets, named for the 1-year-old daughter of developer Joseph Kaempfer (who financed the park in return for density bonuses on an office building in Rosslyn), was dedicated last week.

This park, designed by landscape architect Peter Wilson of the SWA Group of Boston, is divided into two distinct parts: a treeless sequence of rolling, grassy earth berms, and a flat, gravel-covered urban "room" with yellow-painted concrete benches shaded by formal plantings of pin oaks.

The clarity of the design is admirable and the park will be much-used by office workers, but Wilson overdid it when he put in a flat, Plexiglas-mirrored archway between the two sections. A macadam path, complete with yellow highway striping, travels underneath the arch (and continues to a vanishing point in a trompe l'oeil painting on a concrete side wall). These theatrical tidbits of design will, I fear, go stale in time, like last year's fashion magazines.

By contrast, Holt's strong, strange park will, I think, age gracefully and well.