Few people today realize that Alexandria and Georgetown were, in colonial days and the early decades of national independence, among America's leading seaports. Even before Baltimore developed commercially, tobacco and grain made their way by sea from here to Europe.

An echo of those early years will be present today through April 26 with the visit of the 125-foot schooner Spirit of Massachusetts.

She'll be docked at the Gangplank Marina off the Maine Avenue waterfront. Except for some cruises open to the public for a price and some private receptions, including one for the Massachusetts congressional delegation, she'll be open for free public visits.

Built from an historic design for the New England Historic Seaport by a yard in the Boston environ of Charlestown in 1984, she serves as both a school ship and a good-will ambassador for Massachusetts. A two-master, she's typical of what were called the "fast and able" craft used in the Boston and Gloucester fishing fleets of the past century.

This year's tour includes, in addition to Washington, stops at ports from Miami to New York.

Open house times: 9 a.m. to 3 p.m. tomorrow and Sunday, and 10 a.m. to 4 p.m. Monday. Sailings for ticket-holders (adults $20, children $10), scheduled for 2 1/2 hours, will leave at 4 p.m. tomorrow and Sunday. Call Pat Byrn at 554-5000.

Incidentally, the Spirit's master is Bert Rogers, who until last fall was the captain of the locally based schooner Alexandria. Notes From the Time Warp

A current broadcast commercial for Riggs Bank dramatizes the role of Charles C. Glover, a 19th century president of the bank, in creating Potomac Park and its sites for the Lincoln and Jefferson memorials. The announcer intones that in the 1870s, Glover got the inspiration while on a train that had just left Union Station for Richmond.

From Union Station? No way! It wasn't completed until 1907. Glover would have taken the train from the old Baltimore & Potomac station where the National Gallery of Art now stands.

*The shamelessly hyped television miniseries, "Dream West," based on the exploits of soldier-adventurer John Charles Fremont, showed a scene that purported to be Washington in the 1850s. The centerpiece was the illuminated great dome of the Capitol. Just two problems: the dome wasn't completed until the Civil War era, and -- lacking the availability of electricity -- it wasn't illuminated until many years afterward. (Fremont was one of California's first two senators, serving a short term from September 1850 to March 1851.)

Speaking of the Capitol, did you catch the "Gasoline Alley" comic sequence Tuesday in which Rover, the banjo-eyed adoptive grandson of Skeezix, was asked "What's the capitol of the United States?"

" . . . Ask me somethin' I knows," Rover replied.

Rover wasn't so dumb after all. The only correct answer is that it's the building with a dome on its top where the United States Congress meets. Now, if you want to ask what's the capital of the United States where the Capitol is located, maybe Rover knows the answer.