Tall ships and small ships, workboats and yachts, go upon the water for a long or little while and then usually are scrapped or abandoned to time and weather. The backwaters and creeks of the Chesapeake are littered with fine old craft cast adrift when they no longer could earn their keep, and elsewhere around the continent thousands of historic hulls lie rotting.

The heightened sense of history brought about by the bicentennial and the astounding response to last summer's cruise of the tall ships have combined to stimulate a national campaign to save and restore significant campaign to save and restore significant American vessels. The problem is more urgent with ships than with buildings because an untended vessel can sink or crumble beyond recall in a very few months or years. In many cases not a single example remains of craft that once plied American waters by the thousands.

Some 400 of the people who cannot bear to see such ships die gathered in Baltimore over the weekend for the first national conference on maritime preservation, sponsored by the National Trust for Historic Preservation.

The Trust, which only recently expanded its interest from historic buildings to more mobile objects, has launched its maritime program with $400,000 bequeathed by OpSail after the tall ships cruise.Some 65 vessels, from stenwheelers to dories, are on the Turst's list of endangered historic craft and many others have been proposed.

Ships are ruinously expensive to restore, which usually is why they are abandoned in the first place. But money is not the only problem. The ancient skills of the boatbuilder and shipwright, passed from old masters to young apprentices for centuries and even millenia, have all but vanished. Old boatyards are littered with tools that few men can name, much less use.

Problems notwithstanding, some 86 vessels have been saved and at least partly restored, usually throught the efforts of "a handful of people who were not practical and would not listen to reason," as one Trust officer put it.

"But the romance, or majesty, or whatever you call this quality that makes us love old ships, is useful only to the extent that it energizes people and mobilizes money. It's damned hard work, and you can't just hire people to do it, you have to get down in the bilges youself. You have to find the manpower and the money, and then you have to find some way to keep the money coming in, either by opening the ship to the public or putting her back to work, because the minute you get her shipshape she starts deteriorating again."

The audience was packed with people who are facing just such difficulties; listening to a few who have overcome them. The most spectacular success is the famous Delta Queen, last of the working Mississipi steamboats, last chance for anyone to ride the river from Cincinnati to New Orleans and experience some of what Mark Twain wrote about in Life on the Mississipi.

Restorationists have applied to the Trust for a total of $5 million in aid for scores of projects; the salvors of the Queen spent that much rebuilding her "from bilge to radar mast, from stem-plate to monkey-rudder," according to Betty Blake, president of the Delta Queen Steamboat Co.

Even so, it took a national publicity campaign leading to an act of Congress to get the 192-passenger Queen back on the river, because her wooden superstructure of oak, mahogany, teak and ironbark from what was then Siam didn't meet modern federal standards. To tear her tattered teakwork down would have been to "ruin the integrity of the vessel and take us under financially," Blake said.

Back in overnight passenger service along 3,500 miles of river, equipped with space-age fire retardants and every safety device she can carry, the Queen has paid her own way and made it possible for the company to build a 400-passenger steel riverboat replica which also sells out every berth.

"Ships live by keeping their living purpose," said Peter Stanford, president of the National Maritime Historical Society.

Some lucky ships live because a willful man will not let them die, as witness the mighty iron bark Star of India, built in 1863 and once consigned to oblivion. She rest now in the harbor at San Diego, open to the public as a museum piece but in all respects ready for sea.

She was saved by a crew headed by Kenneth D. Reynard Sr., a weathered, beefy man who couldn't be called anything but Captain and who is the very model of a crusty old sea dog. Reynard held the conference spellbound as he gave a brief, gravelly, no-nonsense account of how his Maritime Museum Association of San Diego transformed the Star from a rusting hulk "without asking a dime from any public treasury."

The Star never got a chance to spread her 22,000 square feet of sail in company with the tall ships, alas, because marine insurance runs $7,000 a day. She has gone upon the broad water once, just long enough to get her picture taken.

Conference leaders did not promise the preservationists much more than tears, toil and sweat on their projects, but they did suggest possible sources of financial aid ranging from the Farmers Home Administration to the Tennessee Valley Authority.

The point hammered home again and again was that saving old ships takes dedicated people with callused, skillful hands. "Scholarship will not save us," said Lance Lee of the Bath (Maine) Marine Museum. "Continuity of skills will."

Without such work from all of those present and thousands more, said Bolling Haxall of the Thousand Islands (New York) Shipyard Museum, "our heritage as a maritime people will sink into a pile of rotted timber."