Perhaps greatest among Washington's glories are its parks and the parklike settings of the national memorials.

This spring the city is getting one of each--a brand-new park and a parklike memorial--to add to the distinguished list. John Marshall Park on Pennsylvania Avenue has been completed and will be dedicated on May 10, and finishing touches are being applied to the Memorial for the 56 Signers of the Declaration of Independence, in Constitution Gardens.

The projects are alike in two major respects: Each pays homage to its immediate environment and to the city's varied traditions of landscape architecture, and each, though not without flaw, is worth celebrating.

Otherwise these fine new places are extraordinarily different. John Marshall Park works because of its complex, contrasting qualities. The signers memorial, situated on the kidney-shaped island in the Constitution Gardens lake, is the opposite: a unified, serenely expressive design.

The park, commissioned by the Pennsylvania Avenue Development Corp. and built at a cost of $2.5 million, takes up nearly two acres on the north side of the avenue, across from the Fourth Street entrances to the National Gallery's East and West buildings.

The design by Carol R. Johnson & Associates of Cambridge, Mass., (Carol R. Johnson, principal in charge, with Marion Pressley, job captain) is very Washingtonian in spirit--a piece of linear geometry in the tradition of the 1901 McMillan Commission's City Beautiful plan for the capital's monumental core. At the same time it has some lively Boston touches and, at its edges, it reaches out to another, less formal, design tradition.

The basic concept is straightforward. To climb the 12-foot change in grade between the avenue and C Street, the architects decided to construct three separate platforms--two paved, formal bosques flanking a central greensward that reads as a mini-Mall. This is a pleasing idea although, unfortunately, it doesn't work to perfection. The central grassy plane is too big, or too hard-edged, or perhaps simply too open: The National Capital Planning Commission, exercising its responsiblity to protect the city's important vistas (this one leads from Pennsylvania Avenue to the old City Hall), excised from the original proposal rows of trees on the edges of the greensward.

The architects thought the trees would have improved the vista by focusing it more tightly, and at the same time would have given this "garden room," as they call it, a much-needed sense of enclosure. I did not see that first plan, but it is hard not to believe that the architects were right. The feeling of enclosed intimacy at the center is crucial to the open-closed-open sequence of spaces, so it is a great shame that this area is underplanted.

Other than this major reservation (and a few minor things such as the rigid geometric arrangement of love seat-type benches in the lower bosque) I can only sing the praises of this new park. It is delightful and apt in conception and execution--an adroit, intelligent balancing of contrasting spaces, textures and traditions.

The clean, crisp linearity of the design fixes itself in the mind, but for all that the park is quite inviting. The space stretches the eye in the Washington way, and yet provides places where the eye can rest. The park is at once formal and informal, hard and soft, serene and playful, expansive and intimate.

Among the enticing details: The border plantings are admirably selected and grouped, and the layering of plants, from low to medium to high, softens the hard right angles of the pathway system. The architects have utilized granite sidewalls to great effect, both for visual variety and for sittable places. Inlaid chessboards doubtless will attract players. Paving patterns are simple but nicely woven. The plantings of littleleaf lindens in the upper and lower bosques are appropriately geometrical and urban.

Special features are the sculptures: a sundial copied from one in the Richmond garden of John Marshall (chief justice of the United States from 1801 to 1835, who at one time lived where the park now is); very pretty aquatic bronzes (lily pads, fish, frogs, dragonflies) in the square fountains of the upper bosque, designed by David Phillips; and two bronze chess players seated on a granite sidewall, designed by Lloyd Lillie. Profound these are not, but already they are the hit of the park. Almost invariably people passing through stop to look, and couples photograph each other perching on this knee or that.

The signers memorial is another story altogether. Commissioned by the National Park Service, paid for with $350,000 left over from the Bicentennial Commission, and designed with great tact by Joseph E. Brown (with project manager Cales Givens) of the planning and landscape design firm EDAW Inc., it is a quiet place at peace with the gentle, rolling landscape of Constitution Gardens.

The design, in a way, may be a bit too reticent--the Declaration itself is nowhere reproduced, and foreign tourists, especially, may not get the point--but I have a feeling that in time its moving story will tell itself.

"We didn't want to be too tutorial; we wanted to concentrate upon the signatures themselves, to put those marks in stone," Brown says. The focus of the memorial consists of pink granite blocks, ranged in an ellipse broken at the center, into which the actual signatures, enlarged, have been engraved. The signatures sparkle: they have been pressed with gold leaf.

At the entrance to these rows of stone the last sentence of the Declaration is engraved: "And for the support of this Declaration, with a firm reliance on the protection of divine Providence, we mutually pledge to each other our Lives, our Fortunes and our sacred Honor."

The memorial, with its clear view of the Washington Monument, is fittingly placed. Somehow its horizontality, its utter inauspiciousness, is fitting, too. Its mood is right for the reflective goal, and it suits the landscape. In concept it is not unlike the nearby Vietnam Veterans Memorial: low, harmonious, respectful of the natural environment and symbolic resonance of its position. (Brown points out that plans for this memorial preceded the Vietnam Veterans competition.)

One approaches the memorial across a wooden bridge and enters it via a pathway of smooth granite pavers. The vocabulary of curves--the ellipse of the rugged blocks, the S-curve of a low fieldstone wall that subtly separates the memorial from the rest of the island, the gentle rim of saucer magnolias--is an ideal echo of the meandering informality of Constitution Gardens.

Although not fully planted, already this memorial has become a special place--a peaceful, meaningful park-within-a-park. The happy aspect of the story is that the memorial can only get better with age, as those magnolias and other plants mature. The same thing can be said of John Marshall Park.