Early April is, of course, the ideal time to walk in Washington's parks. It also is the perfect month to drive its parkways -- remnants of a gentler age of the automobile.

The area's first parkway was completed in 1932, just in time to memorialize the bicentennial celebration of George Washington's birth. From the Beltway junction near the Cabin John Bridge all the way to Mount Vernon, this stretch of dual road (extended in the 1950s and again in the 1960s) remains our most beautiful highway, providing splendid first glimpses of the capital city from the high Virginia palisades and, south of Alexandria, an appropriately idyllic introduction to an 18th-century mansion that has become a national monument.

We don't build main roads like this any longer, and though the reasons are, up to a point, understandable, it is nonetheless a great shame. What has been largely lost is the esthetic dimension of road building, and anyone with a mind to test the degree to which the skill -- or is it the will? -- to build beautiful highways has been displaced by sheer expediency need go no farther than the canyonlike corridor of Interstate 66 as it sweeps through Arlington.

I-66 seems to be doing its job of getting people quickly from here to there. Indeed, one of the ironies of its construction is that it can whisk parkway buffs from the city to Skyline Drive (one of the nation's pre-eminent rural pleasure roads, and another product of foresightful 1930s planning) in a scant 60 minutes or so.

But its Arlington section is a catalogue of ugly errors. The curves are unpleasant and jumpy, the bridges that cross it are unlovely, the approaches to it (parlicularly once-pretty Lee Highway) are abysmal, the plantings are minimal at best, and the concrete or metal retaining walls and sound barriers that line the road through much of its Arlington trajectory are, in addition to being ugly, claustrophobic.

Other recent roads demonstrate a similar, though not nearly so precipitous, decline in standards. Interstate 95 north to Baltimore, for instance, constructed during the late 1970s, compares unfavorably with the Baltimore-Washington Parkway (1950s). Partly this is because the latter is a parklike road and the former is not; more importantly, the B-W Parkway blends with the hilly terrain in a beautifully designed sequence of vertical and horizontal curves, while I-95 is a brutal machine that cuts through the land.

The new Dulles Toll Road is not nearly so objectionable as might have been expected -- there is in fact a certain grandeur to the sight of the eight ribbons smoothly coursing through the Virginia hills -- but the main credit, I suspect, is due the designers of the original airport road, so commodiously laid out in the early 1960s. The parallel toll road, though it presses uncomfortably against the edges of the right of way, simply follows this lead.

Problems obviously multiply as the big roads are brought into the city. In Los Angeles, where the freeways were laid out mainly on rights of way established years earlier for rail transportation, the freeway was able to become the primary esthetic. However, such an order is impossible in older cities such as Washington, San Francisco, New Orleans, Boston or Baltimore, where the conflicts between increasing traffic and the delicate existing fabric of the city begot some terrible roads and, not coincidentally, the road-stopping combat of the 1960s.

Washington's inner-city freeways are in fact uniformly unattractive -- the lonely triumphs are mostly negative, such as the halting of the ill-conceived North Central Freeway, or the tunneling of its southern branch underneath the Mall. Even Cloethiel Woodard Smith's handsome stone borders for the E Street Expressway do nothing to mitigate the road's utter superfluity. Still, none of the city's superhighways is ugly in so many ways as I-66 in Arlington, which suggests a regression not only from the time of the parkways, but from the time of the freeways as well.

If all of this sends us back to our parkways with a certain nostalgia, that's okay. After all, it makes great sense to place high values on gifts given, and there is even a certain relevance in the exercise. The parkways (the George Washington Memorial, the Washington-Baltimore, the Suitland, the Rock Creek and Potomac) are under constant threat of unkind change from one source or another, and they need vigilant protection.

In addition, in their form and very purpose the parkways represent an ideal that should not be surrendered lightly. This is nothing more, nor less, than the simple dictum: highways can be beautiful. Or, to put it a slightly different way: driving can be pleasant.

Christopher Tunnard and Boris Pushkarev, who did important studies in the 1960s on the questions of what makes a pleasing highway, wrote, "A freeway cannot be esthetically satisfying unless it is designed to belong where it is put, and not to look like a foreign body in a landscape or cityscape." Each of Washington's parkways -- ribbons of concrete or asphalt that define and are defined by the land they comfortably traverse -- fulfills this principle. They were built with skill and a magnanimous spirit, and they formed part of a comprehensive vision of how best to tie together the various parts of a city or region with important roads.

Much of this vision was not to be. There is, for instance, the matter of Fort Drive, a proposal in the McMillan Commission report in 1902 to link the ring of Civil War forts on the city's northern and eastern ridges. The idea was that "anyone . . . could pick up such a drive at any point and find himself on a continuous, unbroken, easily followed, wooded road, connecting a succession of historic points, each of which has an unusual view that caused its selection as the site for a military fort. It would constitute the most striking and famous parkway in this part of the country . . ."

Now that, I submit, is a public-spirited vision of the highest order. Can you imagine the thrill of the drive, and of the views? In the 1920s and 1930s, with prodding from the National Capital Planning Commission (established in part to oversee completion of the McMillan Commission plan), some land for Fort Drive was acquired, and bits and pieces of it exist -- Military Road in the northwest, Texas Avenue and Fort Davis Drive in Anacostia -- but they are no more than paltry reminders of an opportunity sadly lost.

To those who would say that this example is an irrelevancy left over from the days of the Model T, one can point to the McMillan Commission vision for quay highways along the Anacostia and Potomac shorelines. Had this vision been fulfilled, Washington might have had its own version of Chicago's famous multi-level Wacker Drive, a superb urban road with levels for boats, cars and pedestrians at riverside.

Alas, we do not have it. But we have what we have, and at this time of year the slivers of greening forest along the edges of our parkways are every bit as magical as in the last crisp breath of fall. One can still see through the screen of trees to nearby suburban houses or urban apartments and yet the promise of lush hiding growth is there, so one can readily appreciate the fact of parkway artifice: these special spaces were built in narrow corridors not simply for our convenience, but also for our delight. It is a lesson we shouldn't ignore.