At long last, the historic mile of Pennsylvania Avenue from the Capitol to the White House, so long known simply as "the Avenue," is on the verge of being saved. Beginning with a refurbished Willard Hotel at the 14th Street corner, the Pennsylvania Avenue Development Corporation promises to bring new beauty and vibrancy to the famous throughfare in what might be called the Avenue's fifth incarnation.

It is important, however, that we not let go of everything that has gone before.

Except for the Willard (and after all, the present building is only the "new Willard," built in 1901) there doesn't seem to be a single venerable structure on the Avenue's north side worth saving. And to create the Federal Triangle, the South side was stripped clean of history save for the "old Post Office" erected in the 1890s, and that building is due for a new interior life before long. If one considers the east side of 15th Street facing the Treasury as part of the historic parade route, then Rhodes Tavern at the F Street corner ought to be saved. It is not beyond the wit of architects to restore it as part of that block's redevelopment.

But, what we need somewhere along the Avenue is a room, a gallery, an exhibit hall or some comparable place in which the past can be presented to passers-by. The PADC ought to figure out how to tuck into its plans such a reminder of history.

And what a history.

When Washington became the national capital in 1800, Congress met only briefly each year.Most members left families at home and lived in boarding houses on either side of the Capitol; on the Avenue, such boarding houses lasted at least through Civil War years, interspersed with hotels, mostly between 1st and 7th streets. By 1806 such hostelries were used by post-road travelers between Baltimore and the South. Jackson, Henry Clay, Henry Calhoun, Daniel Webster and other such figures lived at the St. Charles Hotel at 3rd and the Avenue; from the National (originally Gadsbys') at 6th, Andrew Jackson walked to his inauguration. The National Hotel was still standing, though vacant, when I first came to town in the first year of the Franklin Roosevelt administration; there a tablet listed among the hotel's distinguished guests Horace Mann, Alexander H. Stephens, Thaddeus Stevens (but John Wilkes Booth was omitted); there Clay died in 1852.

Across 6th from the National once stood the Indian Queen - one of its many names because of Pocahontas' portrait on its signboard. That was where John Tyler in 1841 took the oath as president when William Henry Harrison died, thus asserting the first vice presidential claim to a full succession to power.

After those early years - the Avenue's first incarnation - the city center became the 7th Street corner. That phase lasted, perhaps, to the turn of the century and the arrival of automobiles. Center Market occupied the current National Archives site at 7th from the 1870s to the 1930s, and there housewives and servants of the affluent came daily for meats from New York, fish from the Potomac, oysters from the Chesapeake and ducks and turkeys from the hinterland.

At what began as 4 1/2 Street but is now called John Marshall Place stood Hotel Fritz Reuter, with a restaurant and rathskellar famous for its terrapin and broiled lobster. Today on the corner (across from the U.S. Court House) is a building, long used by the USO, that was erected by Henry Ford and in which the first Model A's were unveiled for Washingtonians in December 1927. The line of eager viewers stretched up Capitol Hill. On that site the Canadian government will build its new chancery, a diplomatic first for the Avenue.

Almost directly across the Avenue, where the National Gallery stands, was the Baltimore & Potomac Depot, when President Garfield was fatally wounded. The railroad shed intruded onto, and its tracks crossed, the Mall.

Washington's center of life kept moving north and west. Although the Willard and its predecessor hotels have occupied the 14th Street corner since about 1818, it was the Civil War that gave Willard's prominence; there the words to the "Battle Hymn of the Republic" were written, and at least eight presidents and several vice presidents have been among the Willard's guests. Across the street in lovely Pershing Square stood what had begun in 1884 as albaugh's Grand Opera House; it was to become Chase's and finally Poli's, lasting into the early 1930s when the Federal Triangle buildings were completed.

The arrival of that massive collection of bureaucracy marked the Avenue's fourth era. Among the other enterprises it finally ended was Hooker's Division, the famous bordello area along long-gone Ohio Avenue, a street parallel to and south of the Avenue.

Alas, after the Triangle was created, too many of the Avenue's lights began to go out when the bureaucrats went home - "home" first being elsewhere in the city and then increasingly the suburbs. The north side of the Avenue deteriorated with the Great Depression; who can forget (or can we?) Gen. Douglas MacArthur with his aide Maj. Dwight Eisenhower standing at his side, directing the Army in routing the 1932 Bonus Marchers on the Avenue?

I'm for the revival; I like most of the plans so far, although I have serious doubts about the plan to place two pylons on the Avenue to "frame" the White House. I think the PADC ought at least to put them up in wood first, so we can judge their virtues before they become stone.

But my main point is that the PACD ought to see to it that there is some enclave, some quiet spot in which to gather the history, the stories, the photos of the Avenue's great - and, yes, grubby - past for Americans of the future to see and read about. When the Cosmos Club left Lafayette Square for its present residence, it created a portrait of the old square, painted around the walls of one of its rooms. Not everyone can see that bit of history, but it could offer the PADC an idea on how to remember the Avenue in some spot along the grand thoroughfare.

We may never again see a high-wheel bicyle contest, a sleigh masquerade party, horse-drawn third-rail streetcars and many other things that gave sparkle to the Avenue. But there will be successors, and not just the quadrennial parades (or presidential walks). The future will be richer for remembering the past.