BEWARE THE overseas phone call home you make from your hotel room, warns the telephone company. Many hotels abroad impose a surcharge that ranges from 100 to 300 percent of the long-distance rate.

A Rochester, N.Y., tourist made a seven-minute call home from a hotel in Hamburg, West Germany, normally $20 at long-distance rates. The hotel's bill: $110.

A hotel in Paris charged a guest $90 for two $7.50 calls back to the United States, says a spokesman for AT&T Long Lines of Morris Plains, N.J. The hotel claimed the extra $75 helped pay the cost of multilingual operators on the switchboard.

To fight the surcharges, which AT&T figures is costing them millions in potential long-distance revenues, the company is trying to get hotels to agree to "moderate" surcharges at a fixed rate. A number of hotels and chains have joined this "Teleplan," though the company admits it's "an uphill battle."

If you are not checked into a "Teleplan" hotel, advises AT&T, make the call home but be very brief. Get the other party to call you right back. Generally, the surcharge will be based only on the length of the call you originated. In many European cities, you also can make international calls from a telephone center staffed with operators who speak English.

Down on the York River, Virginia archeologists have just surrounded a sunken vessel from Lord Cornwallis' fleet with a steel enclosure, and sometime in July tourists will be able to peer into the watery depths to watch divers excavate the 18th-century relic of the Revolutionary War.

Project leader John Broadwater, director of underwater archeology for the state, believes it is the first time anywhere the general public will be able to witness an underwater dig in progress.

At the moment, the ship, believed to be a brig used for hauling supplies or troops, is buried up to its mast tops in mud 20 feet below the surface of the York and 500 feet from the Yorktown shore. Construction of an 8-foot-wide, 500-foot-long pier to the site was expected to begin last week and is scheduled for completion in early July.

A filtration system is being installed to cleanse the murky water within the enclosure for easier viewing. Right now, says Broadwater, "It's so muddy you can't see anything." The project is sponsored by the Virginia Historic Landmark Commission.

Sightseers will be able to watch the 75-footer with two masts slowly emerge from the mud over the next two or three warm-weather digging seasons. Divers will be at work on weekends to attract the largest number of viewers.

The ship is one of several that Cornwallis, commander of the British forces, lost in the Battle of Yorktown in 1781. It may have been sunk to blockade the port against the approaching French fleet or to prevent American and French forces from seizing it after the British surrender.

Archeologists used sensing devices to discover nine vessels in the river between Glouscester Point and Yorktown. The one chosen "seems to be the best-preserved," says Broadwater. He considers it an important dig because "no one really knows much about a full ocean-going merchant vesssel from the 18th century."